Understanding Newton's Third Law of Motion

What happens when you push against a wall while wearing skates?

• The action force applied to the wall is stronger than the reaction force exerted on you.

• You move closer to the wall because the wheels of the skates.

• You move away from the wall because the wall pushes back against you.

• Your position does not change.

What is Newton's third law of motion?

• The acceleration of an object is equal to the net force acting on the object divided by the object’s mass.

• When one object exerts a force on a second object, the second object exerts a force of the same size but in the opposite direction on the first object.

• If the net force on an object is zero, the motion of the object does not change.

• A force that acts perpendicular to the direction of motion, toward the center of the curve.

What is a force pair?

• Elastic and inelastic forces.

• Acceleration and reaction forces.

• The forces two objects apply to each other.

• A measured of how hard it is to stop a moving object.

What forces are involved in a force pair?

• The action force and the reaction force. The force you apply to an object is the reaction force, and the force that object applies back to you is the action force.

• Speed and acceleration. How fast an object moves in a period of time (speed) after the force applied by the engine, and the decrease in the velocity (acceleration) of the same object due to friction.

• Speed and acceleration. How fast an object moves in a period of time (acceleration) after the force applied by the engine, and the decrease in the velocity (speed) of the same object due to friction.

• The action force and the reaction force. The force you apply to an object is the action force, and the force that object applies back to you is the reaction force.

What is the action force when a rocket lifts off?

• The gas pushing upward on the engine.

• The engine pushing the hot gas out in a downward direction.

What is the reaction force when a rocket lifts off?

• The engine pushing the hot gas out in a downward direction.

• The gas pushing upward on the engine.

Why don’t the forces in a force pair cancel each other?

• Both forces, the action and the reaction forces, when combined are never equal to 0 N.

• The action force is always stronger than the reaction force.

• The reaction force is unnoticeable when the force pair happens in non-solid objects.

• Each force acts on a different object, so they do not cancel out.

What is momentum?

• The tendency of an object to resist a change in its motion, calculated as distance divided by time.

• It is a measure of how hard it is to stop a moving object, calculated as mass times velocity.

• Forces acting on an object that combine and form a net

  force that is not zero are unbalanced forces.

• The combination of all the forces acting on an object.

What is the law of conservation of momentum?

• The resultant momentum of a group of objects stays the same unless outside forces act on the objects.

• The total momentum of a set of objects increases constantly until an outside force is applied.

• The combined momentum of a collection of objects gradually decreases but never becomes 0 kg m/s.

• The total momentum of an array of objects disappears after there is an inelastic collision between them.

If a tennis ball and a bowling ball are rolling at the same speed, which ball is harder to stop?

• There is no difference. The same force is needed to stop both the tennis ball and the bowling ball due to inertia.

• The tennis ball is more difficult to stop because it has less mass and therefore more momentum.

• The bowling ball is harder to stop because it has more mass and consequently a bigger momentum.