Physics: Force

Physics

• Physics is the science of understanding forces

• A force is a push or pull

• General forces include gravity and friction

• Elastic forces include compression, tension, and torque

Gravity

• Gravity is a pull towards the center of the Earth

Gravity (continued)

• Gravity increases with mass

• Weight is a measure of gravity’s force on an object

• Planets with more mass have more gravity

• This is why weight will change on different planets

• Gravity is force that opposes motion

Friction

• Friction is a force that opposes motion between touching surfaces.

• This causes things to wear out such as metal parts in cars and bone joints in our bodies.

• Lubrication, such as oil and grease, help to reduce friction by lubricating the area where two objects come into contact.

• There are two basic types of friction: static and kinetic.

• Static friction is the stronger force of the two.

• Static friction occurs before movement takes place - it resists movement.

• Kinetic friction occurs during movement - it tries to slow or stop movement.

Elastic Forces
Compression

• When forces come together from opposite directions it is called compression.

Tension

• If forces are applied in opposite directions it is called tension.

Torque

• A twisting force is called torque.

Unit

• The unit we use for force is called the Newton (N) from Isaac Newton, the famous physicist.

Calculating Force

To calculate the force of gravity on an object:

1. Convert mass in grams to kilograms (move the decimal to the left three places), and

2. multiply by gravity which on Earth is 9.8.