Chapter 3 - Forces

1.

Describe ways in which a force might change the motion of a body.

  • A force is may make

o   stationary bodies move.

o   moving bodies speed up, slow down or stop.

o   moving bodies change direction.

 2.

Describe how an object released from rest (subjected to air resistance) will eventually fall with constant velocity.

  • Immediately upon release, gravitational force acting on the object causes it to accelerate at 10 m/s2.
  • As the object gains speed, the upward air resistance increases. This will cancel out the downward gravitational force and decrease the acceleration.
  • Eventually the upward air resistance increases to a point where it equals the downward gravitational force.
  • The resultant force acting on the object is now zero. Therefore the acceleration is zero and it continues falling with constant velocity (known as terminal velocity).

 3.

Suggest and explain why a car moves at constant velocity after some time even though the car engine continues providing the same amount of forward driving force (thrust).

  • During acceleration, the car gains speed and the backward resistive forces (air resistance and contact friction with road) increases.
  • It comes to a point where backward resistive forces equals the forward driving force (thrust)
  • The resultant force acting on the object is now zero. Therefore the acceleration is zero and it continues moving with constant velocity (known as terminal velocity).