Does the force of friction helps us to accelerate while running?How does static friction increase with increase in the applied force?Why does the work done by an internal force differ from the work done by external force?A force is exerted on a body, kinetic energy increases but no work is done by the force. Why?Why does a conservative force return the work done against it by a body to that body?Is the work done by friction on an accelerating car zero?The direction of static friction?What is the significance of the sign of work done? Does it affect internal energy also?Running or walking up stairs = same work?Is the work-energy theorem only valid for conservative forces?Sign of the work done by dissipation forces

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Does the force of friction helps us to accelerate while running?


How does static friction increase with increase in the applied force?Why does the work done by an internal force differ from the work done by external force?A force is exerted on a body, kinetic energy increases but no work is done by the force. Why?Why does a conservative force return the work done against it by a body to that body?Is the work done by friction on an accelerating car zero?The direction of static friction?What is the significance of the sign of work done? Does it affect internal energy also?Running or walking up stairs = same work?Is the work-energy theorem only valid for conservative forces?Sign of the work done by dissipation forces






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2












$begingroup$


The question is to find the correct statement:
Cause of increase in kinetic energy while running is due to the work done by friction force without which he cannot run.
OR
Cause of increase in kinetic energy while running is due to the work done by internal forces of the body



Book says 2nd statement is the correct one.
Why is statement 1 not correct and what are internal force?










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  • $begingroup$
    I've added the homework-and-exercises tag. In the future, please use this tag on this type of question.
    $endgroup$
    – Ben Crowell
    8 hours ago

















2












$begingroup$


The question is to find the correct statement:
Cause of increase in kinetic energy while running is due to the work done by friction force without which he cannot run.
OR
Cause of increase in kinetic energy while running is due to the work done by internal forces of the body



Book says 2nd statement is the correct one.
Why is statement 1 not correct and what are internal force?










share|cite|improve this question









New contributor



Animesh Singh is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.






$endgroup$











  • $begingroup$
    I've added the homework-and-exercises tag. In the future, please use this tag on this type of question.
    $endgroup$
    – Ben Crowell
    8 hours ago













2












2








2


1



$begingroup$


The question is to find the correct statement:
Cause of increase in kinetic energy while running is due to the work done by friction force without which he cannot run.
OR
Cause of increase in kinetic energy while running is due to the work done by internal forces of the body



Book says 2nd statement is the correct one.
Why is statement 1 not correct and what are internal force?










share|cite|improve this question









New contributor



Animesh Singh is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.






$endgroup$




The question is to find the correct statement:
Cause of increase in kinetic energy while running is due to the work done by friction force without which he cannot run.
OR
Cause of increase in kinetic energy while running is due to the work done by internal forces of the body



Book says 2nd statement is the correct one.
Why is statement 1 not correct and what are internal force?







homework-and-exercises newtonian-mechanics friction work free-body-diagram






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Animesh Singh is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.










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edited 5 hours ago









Qmechanic

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asked 9 hours ago









Animesh SinghAnimesh Singh

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  • $begingroup$
    I've added the homework-and-exercises tag. In the future, please use this tag on this type of question.
    $endgroup$
    – Ben Crowell
    8 hours ago
















  • $begingroup$
    I've added the homework-and-exercises tag. In the future, please use this tag on this type of question.
    $endgroup$
    – Ben Crowell
    8 hours ago















$begingroup$
I've added the homework-and-exercises tag. In the future, please use this tag on this type of question.
$endgroup$
– Ben Crowell
8 hours ago




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I've added the homework-and-exercises tag. In the future, please use this tag on this type of question.
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8 hours ago










6 Answers
6






active

oldest

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3












$begingroup$

Your body is accelerated by the muscles of the leg extending. That push of the leg muscle is considered an "internal" force, because it's parts of you pushing on other parts of you.



All the kinetic energy your body gains comes from that muscle extension: It's a force exerted over a distance, which does work on you. In turn, that increases your speed and kinetic energy.



Friction is what keeps your foot from moving relative to the ground, so that all the extension acts to push your body. But that friction, by itself, does no work and adds no energy.






share|cite|improve this answer









$endgroup$




















    2












    $begingroup$

    If friction was doing work, running would be a lot more difficult.



    For work, there needs to be force and displacement, and if there's displacement of the applied friction force, that means your feet are slipping on the surface. This slipping obviously takes away from your ability to gain forward motion.



    When you are moving efficiently, there is only static friction between your feet and the ground. This is just a stationary force, and therefore no work can be done by it. The static friction allows you to convert that internal energy into kinetic energy. If the friction did work, it would actually be working against the increase in kinetic energy, via slipping.






    share|cite|improve this answer









    $endgroup$




















      1












      $begingroup$

      Static friction just holds the foot stationary. That is all.



      When you take a step on the ground, the muscles in your leg press your foot backwards and the rest of your body forwards. Since the foot can't go backwards due to static friction, the rest of your body goes much more forwards, because the leg still must stretch as the muscles force it to.



      So, basically, static friction makes it possible for you to push yourself away from the ground. But it isn't the force that actually does it. Just like you can push yourself away from a wall. That makes you speed up, not because the wall supplies any energy to you, but because the energy you put into jolting your arms backwards into the wall results in the rest of your body moving the opposite way since the arms ain't moving backwards.



      This is Newton's 3rd law.






      share|cite|improve this answer











      $endgroup$








      • 1




        $begingroup$
        One of the best examples I can think of to illustrate this is the difficulty of spaceflight. When travelling around Earth, we generally have stuff we can push against to gain kinetic energy from internal forces. When you're in space, there's nothing external to push against, so you have to start pushing against yourself essentially (thus ejecting fuel all the time for propulsion).
        $endgroup$
        – JMac
        6 hours ago


















      0












      $begingroup$

      He wouldn't move anywhere without friction but the kinetic energy would still exist if he were flailing his legs around on wet ice.






      share|cite|improve this answer








      New contributor



      user47014 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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        0












        $begingroup$

        The book statement is correct. Having said that, the first statement is important, because without gravity pulling the runner toward the centre of the Earth, and the friction with the running track surface which this causes, there would be almost no increase in the runner's kinetic energy. He would be like someone in very slippery shoes trying to run on the polished surface of a freshly frozen ice rink, just floundering about and getting nowhere. So it is true to say that friction of running shoes against the ground helps runners to accelerate, but the increase in the runner's kinetic energy is due to the work done by his muscles.






        share|cite|improve this answer









        $endgroup$




















          0












          $begingroup$


          Cause of increase in kinetic energy while running is due to the work
          done by friction force without which he cannot run. OR Cause of
          increase in kinetic energy while running is due to the work done by
          internal forces of the body




          It is the static friction force between the runners feet and the ground that propels the runner forward. See the figure of a runner below showing the forces acting upon him and by him. It is the following static friction force shown in the figure that propels the runner foward.



          $$F_f=F_pushCosθ$$



          In order for the runner not to slip the friction force cannot exceed the maximum static friction force also shown in the figure.



          hope this helps.



          enter image description here






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            6 Answers
            6






            active

            oldest

            votes








            6 Answers
            6






            active

            oldest

            votes









            active

            oldest

            votes






            active

            oldest

            votes









            3












            $begingroup$

            Your body is accelerated by the muscles of the leg extending. That push of the leg muscle is considered an "internal" force, because it's parts of you pushing on other parts of you.



            All the kinetic energy your body gains comes from that muscle extension: It's a force exerted over a distance, which does work on you. In turn, that increases your speed and kinetic energy.



            Friction is what keeps your foot from moving relative to the ground, so that all the extension acts to push your body. But that friction, by itself, does no work and adds no energy.






            share|cite|improve this answer









            $endgroup$

















              3












              $begingroup$

              Your body is accelerated by the muscles of the leg extending. That push of the leg muscle is considered an "internal" force, because it's parts of you pushing on other parts of you.



              All the kinetic energy your body gains comes from that muscle extension: It's a force exerted over a distance, which does work on you. In turn, that increases your speed and kinetic energy.



              Friction is what keeps your foot from moving relative to the ground, so that all the extension acts to push your body. But that friction, by itself, does no work and adds no energy.






              share|cite|improve this answer









              $endgroup$















                3












                3








                3





                $begingroup$

                Your body is accelerated by the muscles of the leg extending. That push of the leg muscle is considered an "internal" force, because it's parts of you pushing on other parts of you.



                All the kinetic energy your body gains comes from that muscle extension: It's a force exerted over a distance, which does work on you. In turn, that increases your speed and kinetic energy.



                Friction is what keeps your foot from moving relative to the ground, so that all the extension acts to push your body. But that friction, by itself, does no work and adds no energy.






                share|cite|improve this answer









                $endgroup$



                Your body is accelerated by the muscles of the leg extending. That push of the leg muscle is considered an "internal" force, because it's parts of you pushing on other parts of you.



                All the kinetic energy your body gains comes from that muscle extension: It's a force exerted over a distance, which does work on you. In turn, that increases your speed and kinetic energy.



                Friction is what keeps your foot from moving relative to the ground, so that all the extension acts to push your body. But that friction, by itself, does no work and adds no energy.







                share|cite|improve this answer












                share|cite|improve this answer



                share|cite|improve this answer










                answered 9 hours ago









                Bob JacobsenBob Jacobsen

                6,86611 silver badges22 bronze badges




                6,86611 silver badges22 bronze badges























                    2












                    $begingroup$

                    If friction was doing work, running would be a lot more difficult.



                    For work, there needs to be force and displacement, and if there's displacement of the applied friction force, that means your feet are slipping on the surface. This slipping obviously takes away from your ability to gain forward motion.



                    When you are moving efficiently, there is only static friction between your feet and the ground. This is just a stationary force, and therefore no work can be done by it. The static friction allows you to convert that internal energy into kinetic energy. If the friction did work, it would actually be working against the increase in kinetic energy, via slipping.






                    share|cite|improve this answer









                    $endgroup$

















                      2












                      $begingroup$

                      If friction was doing work, running would be a lot more difficult.



                      For work, there needs to be force and displacement, and if there's displacement of the applied friction force, that means your feet are slipping on the surface. This slipping obviously takes away from your ability to gain forward motion.



                      When you are moving efficiently, there is only static friction between your feet and the ground. This is just a stationary force, and therefore no work can be done by it. The static friction allows you to convert that internal energy into kinetic energy. If the friction did work, it would actually be working against the increase in kinetic energy, via slipping.






                      share|cite|improve this answer









                      $endgroup$















                        2












                        2








                        2





                        $begingroup$

                        If friction was doing work, running would be a lot more difficult.



                        For work, there needs to be force and displacement, and if there's displacement of the applied friction force, that means your feet are slipping on the surface. This slipping obviously takes away from your ability to gain forward motion.



                        When you are moving efficiently, there is only static friction between your feet and the ground. This is just a stationary force, and therefore no work can be done by it. The static friction allows you to convert that internal energy into kinetic energy. If the friction did work, it would actually be working against the increase in kinetic energy, via slipping.






                        share|cite|improve this answer









                        $endgroup$



                        If friction was doing work, running would be a lot more difficult.



                        For work, there needs to be force and displacement, and if there's displacement of the applied friction force, that means your feet are slipping on the surface. This slipping obviously takes away from your ability to gain forward motion.



                        When you are moving efficiently, there is only static friction between your feet and the ground. This is just a stationary force, and therefore no work can be done by it. The static friction allows you to convert that internal energy into kinetic energy. If the friction did work, it would actually be working against the increase in kinetic energy, via slipping.







                        share|cite|improve this answer












                        share|cite|improve this answer



                        share|cite|improve this answer










                        answered 8 hours ago









                        JMacJMac

                        9,8202 gold badges23 silver badges37 bronze badges




                        9,8202 gold badges23 silver badges37 bronze badges





















                            1












                            $begingroup$

                            Static friction just holds the foot stationary. That is all.



                            When you take a step on the ground, the muscles in your leg press your foot backwards and the rest of your body forwards. Since the foot can't go backwards due to static friction, the rest of your body goes much more forwards, because the leg still must stretch as the muscles force it to.



                            So, basically, static friction makes it possible for you to push yourself away from the ground. But it isn't the force that actually does it. Just like you can push yourself away from a wall. That makes you speed up, not because the wall supplies any energy to you, but because the energy you put into jolting your arms backwards into the wall results in the rest of your body moving the opposite way since the arms ain't moving backwards.



                            This is Newton's 3rd law.






                            share|cite|improve this answer











                            $endgroup$








                            • 1




                              $begingroup$
                              One of the best examples I can think of to illustrate this is the difficulty of spaceflight. When travelling around Earth, we generally have stuff we can push against to gain kinetic energy from internal forces. When you're in space, there's nothing external to push against, so you have to start pushing against yourself essentially (thus ejecting fuel all the time for propulsion).
                              $endgroup$
                              – JMac
                              6 hours ago















                            1












                            $begingroup$

                            Static friction just holds the foot stationary. That is all.



                            When you take a step on the ground, the muscles in your leg press your foot backwards and the rest of your body forwards. Since the foot can't go backwards due to static friction, the rest of your body goes much more forwards, because the leg still must stretch as the muscles force it to.



                            So, basically, static friction makes it possible for you to push yourself away from the ground. But it isn't the force that actually does it. Just like you can push yourself away from a wall. That makes you speed up, not because the wall supplies any energy to you, but because the energy you put into jolting your arms backwards into the wall results in the rest of your body moving the opposite way since the arms ain't moving backwards.



                            This is Newton's 3rd law.






                            share|cite|improve this answer











                            $endgroup$








                            • 1




                              $begingroup$
                              One of the best examples I can think of to illustrate this is the difficulty of spaceflight. When travelling around Earth, we generally have stuff we can push against to gain kinetic energy from internal forces. When you're in space, there's nothing external to push against, so you have to start pushing against yourself essentially (thus ejecting fuel all the time for propulsion).
                              $endgroup$
                              – JMac
                              6 hours ago













                            1












                            1








                            1





                            $begingroup$

                            Static friction just holds the foot stationary. That is all.



                            When you take a step on the ground, the muscles in your leg press your foot backwards and the rest of your body forwards. Since the foot can't go backwards due to static friction, the rest of your body goes much more forwards, because the leg still must stretch as the muscles force it to.



                            So, basically, static friction makes it possible for you to push yourself away from the ground. But it isn't the force that actually does it. Just like you can push yourself away from a wall. That makes you speed up, not because the wall supplies any energy to you, but because the energy you put into jolting your arms backwards into the wall results in the rest of your body moving the opposite way since the arms ain't moving backwards.



                            This is Newton's 3rd law.






                            share|cite|improve this answer











                            $endgroup$



                            Static friction just holds the foot stationary. That is all.



                            When you take a step on the ground, the muscles in your leg press your foot backwards and the rest of your body forwards. Since the foot can't go backwards due to static friction, the rest of your body goes much more forwards, because the leg still must stretch as the muscles force it to.



                            So, basically, static friction makes it possible for you to push yourself away from the ground. But it isn't the force that actually does it. Just like you can push yourself away from a wall. That makes you speed up, not because the wall supplies any energy to you, but because the energy you put into jolting your arms backwards into the wall results in the rest of your body moving the opposite way since the arms ain't moving backwards.



                            This is Newton's 3rd law.







                            share|cite|improve this answer














                            share|cite|improve this answer



                            share|cite|improve this answer








                            edited 6 hours ago

























                            answered 6 hours ago









                            SteevenSteeven

                            28.7k8 gold badges68 silver badges118 bronze badges




                            28.7k8 gold badges68 silver badges118 bronze badges







                            • 1




                              $begingroup$
                              One of the best examples I can think of to illustrate this is the difficulty of spaceflight. When travelling around Earth, we generally have stuff we can push against to gain kinetic energy from internal forces. When you're in space, there's nothing external to push against, so you have to start pushing against yourself essentially (thus ejecting fuel all the time for propulsion).
                              $endgroup$
                              – JMac
                              6 hours ago












                            • 1




                              $begingroup$
                              One of the best examples I can think of to illustrate this is the difficulty of spaceflight. When travelling around Earth, we generally have stuff we can push against to gain kinetic energy from internal forces. When you're in space, there's nothing external to push against, so you have to start pushing against yourself essentially (thus ejecting fuel all the time for propulsion).
                              $endgroup$
                              – JMac
                              6 hours ago







                            1




                            1




                            $begingroup$
                            One of the best examples I can think of to illustrate this is the difficulty of spaceflight. When travelling around Earth, we generally have stuff we can push against to gain kinetic energy from internal forces. When you're in space, there's nothing external to push against, so you have to start pushing against yourself essentially (thus ejecting fuel all the time for propulsion).
                            $endgroup$
                            – JMac
                            6 hours ago




                            $begingroup$
                            One of the best examples I can think of to illustrate this is the difficulty of spaceflight. When travelling around Earth, we generally have stuff we can push against to gain kinetic energy from internal forces. When you're in space, there's nothing external to push against, so you have to start pushing against yourself essentially (thus ejecting fuel all the time for propulsion).
                            $endgroup$
                            – JMac
                            6 hours ago











                            0












                            $begingroup$

                            He wouldn't move anywhere without friction but the kinetic energy would still exist if he were flailing his legs around on wet ice.






                            share|cite|improve this answer








                            New contributor



                            user47014 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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                            $endgroup$

















                              0












                              $begingroup$

                              He wouldn't move anywhere without friction but the kinetic energy would still exist if he were flailing his legs around on wet ice.






                              share|cite|improve this answer








                              New contributor



                              user47014 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                              Check out our Code of Conduct.





                              $endgroup$















                                0












                                0








                                0





                                $begingroup$

                                He wouldn't move anywhere without friction but the kinetic energy would still exist if he were flailing his legs around on wet ice.






                                share|cite|improve this answer








                                New contributor



                                user47014 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                                Check out our Code of Conduct.





                                $endgroup$



                                He wouldn't move anywhere without friction but the kinetic energy would still exist if he were flailing his legs around on wet ice.







                                share|cite|improve this answer








                                New contributor



                                user47014 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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                                share|cite|improve this answer






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                                answered 9 hours ago









                                user47014user47014

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                                    0












                                    $begingroup$

                                    The book statement is correct. Having said that, the first statement is important, because without gravity pulling the runner toward the centre of the Earth, and the friction with the running track surface which this causes, there would be almost no increase in the runner's kinetic energy. He would be like someone in very slippery shoes trying to run on the polished surface of a freshly frozen ice rink, just floundering about and getting nowhere. So it is true to say that friction of running shoes against the ground helps runners to accelerate, but the increase in the runner's kinetic energy is due to the work done by his muscles.






                                    share|cite|improve this answer









                                    $endgroup$

















                                      0












                                      $begingroup$

                                      The book statement is correct. Having said that, the first statement is important, because without gravity pulling the runner toward the centre of the Earth, and the friction with the running track surface which this causes, there would be almost no increase in the runner's kinetic energy. He would be like someone in very slippery shoes trying to run on the polished surface of a freshly frozen ice rink, just floundering about and getting nowhere. So it is true to say that friction of running shoes against the ground helps runners to accelerate, but the increase in the runner's kinetic energy is due to the work done by his muscles.






                                      share|cite|improve this answer









                                      $endgroup$















                                        0












                                        0








                                        0





                                        $begingroup$

                                        The book statement is correct. Having said that, the first statement is important, because without gravity pulling the runner toward the centre of the Earth, and the friction with the running track surface which this causes, there would be almost no increase in the runner's kinetic energy. He would be like someone in very slippery shoes trying to run on the polished surface of a freshly frozen ice rink, just floundering about and getting nowhere. So it is true to say that friction of running shoes against the ground helps runners to accelerate, but the increase in the runner's kinetic energy is due to the work done by his muscles.






                                        share|cite|improve this answer









                                        $endgroup$



                                        The book statement is correct. Having said that, the first statement is important, because without gravity pulling the runner toward the centre of the Earth, and the friction with the running track surface which this causes, there would be almost no increase in the runner's kinetic energy. He would be like someone in very slippery shoes trying to run on the polished surface of a freshly frozen ice rink, just floundering about and getting nowhere. So it is true to say that friction of running shoes against the ground helps runners to accelerate, but the increase in the runner's kinetic energy is due to the work done by his muscles.







                                        share|cite|improve this answer












                                        share|cite|improve this answer



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                                        Michael WalsbyMichael Walsby

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                                            $begingroup$


                                            Cause of increase in kinetic energy while running is due to the work
                                            done by friction force without which he cannot run. OR Cause of
                                            increase in kinetic energy while running is due to the work done by
                                            internal forces of the body




                                            It is the static friction force between the runners feet and the ground that propels the runner forward. See the figure of a runner below showing the forces acting upon him and by him. It is the following static friction force shown in the figure that propels the runner foward.



                                            $$F_f=F_pushCosθ$$



                                            In order for the runner not to slip the friction force cannot exceed the maximum static friction force also shown in the figure.



                                            hope this helps.



                                            enter image description here






                                            share|cite|improve this answer











                                            $endgroup$

















                                              0












                                              $begingroup$


                                              Cause of increase in kinetic energy while running is due to the work
                                              done by friction force without which he cannot run. OR Cause of
                                              increase in kinetic energy while running is due to the work done by
                                              internal forces of the body




                                              It is the static friction force between the runners feet and the ground that propels the runner forward. See the figure of a runner below showing the forces acting upon him and by him. It is the following static friction force shown in the figure that propels the runner foward.



                                              $$F_f=F_pushCosθ$$



                                              In order for the runner not to slip the friction force cannot exceed the maximum static friction force also shown in the figure.



                                              hope this helps.



                                              enter image description here






                                              share|cite|improve this answer











                                              $endgroup$















                                                0












                                                0








                                                0





                                                $begingroup$


                                                Cause of increase in kinetic energy while running is due to the work
                                                done by friction force without which he cannot run. OR Cause of
                                                increase in kinetic energy while running is due to the work done by
                                                internal forces of the body




                                                It is the static friction force between the runners feet and the ground that propels the runner forward. See the figure of a runner below showing the forces acting upon him and by him. It is the following static friction force shown in the figure that propels the runner foward.



                                                $$F_f=F_pushCosθ$$



                                                In order for the runner not to slip the friction force cannot exceed the maximum static friction force also shown in the figure.



                                                hope this helps.



                                                enter image description here






                                                share|cite|improve this answer











                                                $endgroup$




                                                Cause of increase in kinetic energy while running is due to the work
                                                done by friction force without which he cannot run. OR Cause of
                                                increase in kinetic energy while running is due to the work done by
                                                internal forces of the body




                                                It is the static friction force between the runners feet and the ground that propels the runner forward. See the figure of a runner below showing the forces acting upon him and by him. It is the following static friction force shown in the figure that propels the runner foward.



                                                $$F_f=F_pushCosθ$$



                                                In order for the runner not to slip the friction force cannot exceed the maximum static friction force also shown in the figure.



                                                hope this helps.



                                                enter image description here







                                                share|cite|improve this answer














                                                share|cite|improve this answer



                                                share|cite|improve this answer








                                                edited 5 hours ago

























                                                answered 6 hours ago









                                                Bob DBob D

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                                                    Кастелфранко ди Сопра Становништво Референце Спољашње везе Мени за навигацију43°37′18″ СГШ; 11°33′32″ ИГД / 43.62156° СГШ; 11.55885° ИГД / 43.62156; 11.5588543°37′18″ СГШ; 11°33′32″ ИГД / 43.62156° СГШ; 11.55885° ИГД / 43.62156; 11.558853179688„The GeoNames geographical database”„Istituto Nazionale di Statistica”проширитиууWorldCat156923403n850174324558639-1cb14643287r(подаци)