The Gravitational Force GRAVITY The force that attracts

The Gravitational Force

GRAVITY • The force that attracts a body towards the center of the earth, or towards any other physical body having mass • The Sun’s gravity is what holds our solar system together.

Everyone Stand Up • • Now, JUMP! What happened? Why did it happen? Would we experience the same outcome if we JUMPED on the moon?

Universal Gravitation • Sir Isaac Newton theorized the Law of Gravitation – Force of gravity acts between all objects – If mass increases, the force of gravity increases – If distance increases, the force of gravity decreases

Mass • Mass is the amount of matter in an object. • Mass is measured in kilograms. • Mass stays the same wherever you are.

Weight • Weight is the measure of the gravitational force acting on an object. • Weight can be measured in Newtons (N) or pounds (lbs) • Weight does not stay the same. It changes when gravity changes.

With your partner, compare and contrast Mass vs. Weight

Mass and Weight • • A 10 -kilogram rock has a mass of 10 kilograms no matter where it is in the universe. A 10 -kilogram rock’s weight however, can vary greatly depending on where it is.

Weight (N) W = mg Gravity ( 9. 8 N/kg) Mass (kg)

What do I need to know if I want to figure out how much our Global Science book weighs? W=mxg • What do we need to know? mass 9. 8 N/kg

Calculate weight Our textbook has a mass of 2. 2 kilograms. What is its weight on Earth? (9. 8 N/kg) • • • G: Given U: Undefined E: Equation S: Substitution S: Solve

Calculate weight Our textbook has a mass of 2. 2 kilograms. What is its weight on Earth? (9. 8 N/kg) • G mass= 2. 2 kg g= 9. 8 N/kg • U W (weight) • E W= m x g • S W = 2. 2 kg x 9. 8 N/kg • S W = 21. 56 N

Calculate weight Our textbook has a mass of 2. 2 kilograms. What is its weight on Mars? (g = 3. 7 N/kg) • G m= 2. 2 kg g = 3. 7 N/kg • U W (weight) • E W=mxg • S W= (2. 2 kg) x (3. 7 N/kg) • S W = 8. 14 N

Our textbook has a mass of 2. 2 kilograms. If the textbook weighs 19. 6 Newtons on Venus, what is the strength of gravity on that planet? • G m= 2. 2 kg W = 19. 6 N • U g (gravity) • E W= m x g • S 19. 6 N = 2. 2 kg x g 19. 6 N/ 2. 2 kg = g • S 8. 91 N/kg = g

Now, you try a few!

Gravity and Motion

Solve for the mass. Problem of the person Challenge FIRST! • G W= 490 N g = 9. 8 N/kg • How much would a person • U m • E W= m x g • S 490 N= m x 9. 8 N/kg • S 50 kg = m who weighs 490 N on Earth weigh on Jupiter? • The value of g at the top of Jupiter’s atmosphere is 23 N/kg. • (Since Jupiter may not actually have a surface, “on” means at the top of the atmosphere. )

Challenge Problem • G m = 50 kg g = 23 N/kg • U W • E w= m x g • S w= (50 kg) (23 N/kg) • S w = 1, 150 N • How much would a person who weighs 490 N on Earth weigh on Jupiter? • The value of g at the top of Jupiter’s atmosphere is 23 N/kg. • (Since Jupiter may not actually have a surface, “on” means at the top of the atmosphere. )

Free Fall and Weightlessness • An elevator is accelerating downward at 9. 8 m/sec 2. • The scale feels no force because it is falling away from your feet at the same rate you are falling. • As a result, you are weightless.