Newton's Third Law

	                                     Name:  ____________________________

A common (but confusing) statement of Newton's Third Law is For every action there is an equal and opposite reaction. In this activity you will measure forces with force sensors and try to understand the real meaning of Newton's Third Law.

Predictions

1.Two objects, a truck on the left, and a car on the right, are on a horizontal rough surface (i.e. there is plenty of friction) and are in contact. The vehicles can have their motors on or their brakes applied, or be in neutral. When the truck and car are in contact, there is a horizontal contact force between them, meaning that the truck pushes or pulls on the car, and the car pushes or pulls on the truck. Compare the magnitudes of these two forces in different situations. All motion is along a straight line.

In Parts (a) to (d) vehicles are of equal mass, in Parts (e) and (f) the truck is much more massive than the car.

Discuss your answers with the others in your group and record your consensus answers.


   Situation               Magnitude of force                Measurements
                             of car on truck is
                               < or = or > 
                             force of truck on car
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 Equal mass vehicles    |                               |             
   push without motion  |                               |             
                        |                               |
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 Equal mass vehicles    |                               |             
   truck pushes car     |                               |             
   at const speed       |                               |
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 Equal mass vehicles    |                               |             
   truck pushes car     |                               |             
   both accel to right  |                               |
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 Equal mass vehicles    |                               |             
   truck pushes car     |                               |             
   as car brakes        |                               |
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 Massive truck runs     |                               |             
   into light car as    |                               |             
   both travel to right |                               |
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 Light car runs into    |                               |             
   massive truck as     |                               |             
   both travel to right |                               |
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