### Year 7 Physics

Introduction to Forces
Contact Forces
Non-Contact Forces
Levers
Wheels & Axles and Pulleys

# 2 | Changes In Speed

## Changes In Speed

• Forces can cause objects to move faster or slower. That is, forces can cause either an increase in speed or a decrease in speed.
• An increase in speed is known as acceleration.
• This may involve an object that is initially stationary (not moving) or an object that is already moving.
• Example 1
• If you jump out of a plane, you will fall with increasing speed.
• Example 2
• If you start pedalling harder when riding your bike, your speed will increase.
• A decrease in speed is known as deceleration.
• If the force causing the deceleration continues for long enough, it will cause the object to stop moving.
• Example 1
• If a rolling ball approaches an upwards slope, its speed will decrease.
• Example 2
• If you apply the brakes on your bike, your speed will decrease. If you keep applying your brakes, you will eventually come to a stop.

Forces can cause an increase in speed, known as acceleration, or a decrease in speed, known as deceleration.