Gravity Goal of the class To learn about

Gravity

Goal of the class • To learn about the properties of gravity • Question of the day: What factors affect gravity?

Discussion • Which way is up? • Which way is down? • Why?

Gravity • Gravity is an attractive force that pulls objects towards each other. • Gravity is a force that affects all objects universally. • Anything with mass feels the force of gravity.

Gravity • Newton discovered the laws of gravitation. Sir. Isaac Newton

Gravity • His law states that any 2 objects are attracted to each other no matter how big or how far away they are. • Then why are you not pulled towards me? You are! But the force is so tiny that you would never feel it.

Factors Affecting Gravity • There are 2 factors that affect gravity 1) Mass is a measure of how much matter an object has (how much stuff). - The force of gravity gets stronger with more mass 2) Distance – the further apart 2 objects are, the lower the force of gravity. - For a spaceship travelling to Mars, the attraction to the Earth decreases and the attraction to Mars increases as it gets closer.

Factors Affecting Gravity

Mass vs. Weight • How much do you weigh? • Weight and mass are NOT the same thing. • The mass of an object is the amount of matter in an object. • The weight of an object is the force of gravity affecting that object. • Weight can change from planet to planet

Mass vs. Weight The astronaut’s mass is always 120 kg but his weight changes.

Freefall • When gravity is the only force the object is in freefall. • An object will go into free fall if released in air. • This is because of an unbalanced force acting on the object • All objects freefall at the same speed! • Objects slow down due to air resistance.

Terminal Velocity • An object will continue to speed up until it hits it’s terminal velocity • Terminal velocity is caused by a cushion of air particles that push against the falling object • The greater the mass, the higher the terminal velocity

Terminal Velocity

Projectile Motion A ball that is shot horizontally will hit the ground at the same time as a ball dropped vertically. They both have a single force acting on them, gravity.

Vocabulary • Weight: the force on the object due to gravity • Air resistance : a force opposing the motion through air • Terminal velocity: the maximum speed of an object falling when air resistance forces balances with gravity

Questions

Homework set #7 • Read chapter on Forces and Friction • Workbook pages 20 -23 • Finish Lab write up