Force and Motion

Unbalanced forces are forces that cause an object to move or change its motion. They are not equal in size and opposite in direction.

Balanced forces are forces that are equal in size and opposite in direction. They do not cause a change in motion.

Friction is a force that opposes the motion of an object. It occurs when two surfaces rub against each other.

Gravity is a force that pulls objects toward each other. It keeps us on the ground and causes objects to fall.

Friction can slow down or stop the motion of an object. More friction means less motion.

When a soccer ball is kicked, an unbalanced force is applied, causing the ball to move.

A ball rolls down a hill because of gravity, which pulls it downward.

An advantage of low friction is that it allows ice skaters to glide smoothly and quickly on the ice.

An example of balanced forces is when a dog pulls on a leash while a boy pulls back, and neither moves.

Unbalanced forces cause an object to accelerate, change direction, or change speed.