Question

The following objects all have a net force of zero Newtons and are therefore in equilibrium. In each case some forces acting on the object are provided. Discuss the total number of forces acting on the object and add the missing forces. You may elect to choose from the provided list of forces, but feel free to discuss/provide a force that is not listed, if you feel your explanation is better.

List of possible forces:

• Weight (The pull of gravity)
• GRF (Ground Reaction Force ; sometimes also called the normal force)
• Static Friction
• Kinetic Friction
• Air Resistance
• Pushing Force
• Tension

Case I:

• A formula 1 car moves at constant velocity along a straight portion of the track.
  Forces provided:
  • Weight of the car
  • Forward push of the car's engine

Case II:

• The same car from Case I is now sitting in pit lane to get it's tires changed
  Forces provided:
  • Weight of the car

Case III:

• An athlete gets ready to climb a vertical rope. He grabs the rope and slightly pulls on it, but he does not yet leave the ground.
  Forces provided:
  • Weight of the athlete  

Case IV:

• A Football player pushing against a sled during practice (see Figure 3.10 in the textbook). The player is unable to get the sled to move despite his effort. Consider forces on the sled as well as on the pushing player.
  Forces provided:
  • Weight of the player
  • Weight of the sled
  • Push of the player against the sled

Answer 1

case 1 - since the car is moving with constant velocity, we will also have a static friction force. along with this, there will be a ground reaction force.

case 2 - there will be a ground reaction force along with a static friction force

case 3 - contact force between the rope and athlete, the internal force generated by the strength of the athlete

case 4 - on player - push of the sled against the player, static friction force between the ground and the player, normal reaction force between the ground and the player

on sled - Push of the player against the sled, normal reaction force between the ground and the sled, static friction force between the ground and the sled