Newton's Third Law

What does Newton's third law state?

Answer explanation

for every action, there is an equal and opposite reaction between interacting objects.

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^{What does action-reaction mean?}

Answer explanation

when a force acts upon something, there is an equal force acting the other way.

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If an object srikes another object, the objects move in opposite directions, but why don't they move the same opposite distance?

Answer explanation

because the mass and composition of the objects affect the object’s actual movement.

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Two metal spheres are suspended on wires so that they hang next to each other, just touching. Sphere X is raised to a certain height and released. Without friction or air resistance, describe what would happen to Sphere Y.

Answer explanation

Sphere Y would swing out in the opposite direction (to the right) to the same original height as Sphere X.

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A 500 N girl standing on a dock exerts a force of 100 N on a sailboat as she pushes it away from the dock. Describe the amount of force that the sailboat exerts on the girl.

Answer explanation

the sailboat will exert 100 N of force back on the girl.

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Identify the action and reaction forces of a rocket blasting off.

Answer explanation

The action of the rocket is the expelling of gas from the engine. The reaction is the movement of the rocket in the opposite direction.

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Engineers have to think about safety in the cars they design. Describe how a vehicle restraint, such as a seat belt, shows Newton’s third law of action, which is reaction, when it helps keep you safe in a car crash.

Answer explanation

If the car gets into an accident, the seat belt holds you in place. The seat belt is applying a force to your body, and your body is applying a force to the seat belt. If the car stopped and you did not have the seat belt on, you would continue to move forward at the same speed at which the car was traveling.

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The action of the rocket is the expelling of gas from the engine. The reaction is the movement of the rocket in the opposite direction.

• 100 Newtons, same direction

• 
  100 Newtons, opposite direction

• 
  200 Newtons, same direction

• 
  200 Newtons, opposite direction

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According to Newton’s Third Law, if someone jumps off a skateboard, the skateboard will roll backwards because -

• the mass of the skateboard is the same as the mass of the person jumping off.

• the pull of gravity on the person is the same as on the skateboard, regardless of size.

• 
  the air resistance on the person is great and the friction on the skateboard is small.

• 
  for the force that sent the person forward, there is an equal force pushing back on the skateboard.

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The nozzle of a rocket is pointed downward so that as fuel is ignited, the exhaust pushes downward. Why is this arrangement necessary for a rocket to function properly?

• 
  As fuel is combusted, the rocket pushes the gases backward and the gases push the rocket forward.

• The rocket is protected from the heat of the exhaust.

• 
  Burned fuel can be collected on the ground.

• This allows the rocket to be steered properly.

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