Chapter 2 Sec 2 Friction and Gravity Friction

Chapter 2 Sec. 2 Friction and Gravity

Friction Forces • Friction is caused by the touching of two objects • Will cause an object to slow down and finally stop • The rougher the surface the higher the friction.

The Good Friction • Friction allows us to walk – friction between the ground and our shoes • Allows car to travel and stop – friction between tires and the road

Types of Friction • Static Friction – Friction between nonmoving objects. • Sliding Friction – Friction between objects that slide past each other. • Rolling Friction – Friction between objects that roll.

Gravity • All objects exert a gravitational force. • The amount depends on the amount of matter. • Gravity keeps us on the ground because the Earth has a lot of matter.

What Determines Gravity • Gravity = Mass(m 1) x Mass(m 2) distance (d 2) § If the objects are massive then gravity is larger. § If the objects are far apart then the gravity is less.

Gravity on Earth • All objects fall to Earth at the same rate. • The acceleration due to gravity is 9. 8 m/s 2. • For calculation purposes we will say the acceleration is 10 m/s 2

Gravity on Earth Cont’d • For every second an object falls to Earth, its velocity increases by 10 m/s. • If a rock falls for 8 seconds, How fast will it be traveling?

Weight vs. Mass • Weight measures how gravity affects mass. • Mass is the amount of matter in the object. • Your scale tells you how earth’s gravity is affecting you.

Air Resistance • Air resistance opposes the motion of objects through the air. • Everything on earth would fall at the exact same speed if it wasn’t for air resistance. • Air resistance depends on the speed, size, and shape of an object.