CHAPTER 9 — Application of Forces & Transfer of Energy

What is a force?

A push or pull.

What are contact forces?

Forces that act when two objects are touching.

What are non-contact forces?

Forces that act between objects without them touching.

Give two examples of contact forces.

Friction and air resistance.

Give two examples of non-contact forces.

Gravitational force and magnetic force.

What is a balanced force?

Forces acting on an object that are equal in size and opposite in direction, giving a resultant force of zero.

What happens when forces on an object are balanced?

The object remains at rest or continues moving at constant speed in a straight line.

What is an unbalanced force?

Forces that result in a non-zero resultant force.

What happens when forces on an object are unbalanced?

The object changes its motion.

What is the resultant force?

The overall force acting on an object after all the forces are combined.

What is work done?

Work is done when a force causes an object to move in the direction of the force.

Is work done on a rider holding onto a rope during wakeboarding?

No, if there is no displacement in the direction of the force exerted by the rope.

Why is no work done on the rider when holding onto the rope?

There is no displacement in the direction of the force exerted by the rope.

What is energy?

The capacity to do work.

State the law of conservation of energy.

Energy cannot be created or destroyed. It can only be transferred from one form to another.

What happens to gravitational potential energy when an object falls?

It is transferred to kinetic energy.

What happens to kinetic energy when a moving object slows down?

It is transferred mainly to thermal energy, with some possibly transferred to sound.