The GravitationalForce

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 andcontrast 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

W = mg

Gravity ( 9.8N/kg)

Mass (kg)

Weight (N)

What do I need to know if I want to figure out how much our Global Science book weighs?

• What do we need to know?W = m x g

mass

GRAVITY OF EARTH9.8 N/kg

Calculate weight

• G: Given• U: Undefined• E: Equation• S: Substitution• S: Solve

Our textbook has a mass of 2.2 kilograms. What is its weight on Earth? (9.8N/kg)

Calculate weight

• G mass= 2.2kg 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

Our textbook has a mass of 2.2 kilograms. What is its weight on Earth? (9.8N/kg)

Calculate weight

• G m= 2.2 kg g = 3.7 N/kg

• U W (weight)

• E W = m x g

• S W= (2.2 kg) x (3.7 N/kg)

• S W = 8.14 N

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 W = 19.6 N

• U g (gravity)

• E W= m x g

• S 19.6 N = 2.2kg x g 19.6 N/ 2.2kg = g

• S 8.91 N/kg = g

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?

Now, you try a few!

Gravity and Motion

Challenge Problem

• 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.)

• G W= 490 N g = 9.8N/kg

• U m

• E W= m x g

• S 490N= m x 9.8N/kg

• S 50 kg = m

Solve for the mass of the personFIRST!

Challenge Problem

• 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.)

• G m = 50 kg g = 23N/kg

• U W

• E w= m x g

• S w= (50 kg) (23N/kg)

• S w = 1,150 N

Free Fall and Weightlessness

• An elevator is accelerating downward at 9.8 m/sec2. • 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.