Gravity, Weight, Mass, Falling Objects, and Centripetal Force

Law of Gravitation

Law of GravitationAny 2 masses exert an attractive

force on each other.Force of gravity increases with

mass and decreases with distance.

Weight vs. Mass

Weight vs. MassWeight is the gravitational force

exerted on an object by the Earth.Weight is a force, and mass is a

measure of the amount of matter an object contains.

Your mass is the same no matter where in the universe you are, but your weight will vary because of gravity.

Calculating WeightWeight is your mass multiplied by

the acceleration due to gravity (g) or 9.8 m/s2.

The formula for weight is:weight = mass x g

Where g = 9.8 m/s2

Weight and Mass

Celestial BodyGravitation

Factor Relative to Earth

Sun 27.9Mercury 0.38

Venus 0.91Earth 1Moon 0.17Mars 0.38

Jupiter 2.54Saturn 1.08Uranus 0.91

Neptune 1.19Pluto 0.06

Falling Objects

Air Resistance• The air resistance of an object

depends on its size, shape, and speed.• Air resistance and NOT the mass of an

object is why certain things fall more quickly than others.

• In a vacuum, there is NO air resistance, so all things fall at the same rate.

In a Vacuum

Exit Ticket

1. Why do you feel the force of attraction between you and the Earth, but not between you and your pencil?

2. What is the difference between weight and mass?

3. What is a vacuum and how do objects fall differently in a vacuum?

Projectile MotionThe path that an object takes when it

is thrown or shot through the air.This path is due to Earth’s

gravitational pull and the object’s own inertia.

Projectile Motion

Terminal VelocityAs an object falls, it accelerates and

its speed increases as does the force of air resistance.

The force of air resistance increases until it cancels out the force of gravity.

When the forces are balanced, the object no longer accelerates, so it reaches a constant speed called its terminal velocity.

Centripetal Force and g’s

Centripetal ForceCentripetal force is an unbalanced

force pushing or pulling an object towards the center of a circle.

Centripetal acceleration is acceleration towards the center of a curved or circular path.

Centripetal Force examplesfrom physicsclassroom.com

As a car makes a turn, the force of friction acting

upon the turned wheels of the car provides centripetal force required for circular

motion.

As a bucket of water is tied to a string and spun in a circle, the tension force acting upon the bucket provides the centripetal

force required for circular motion.

As the moon orbits the Earth, the force of gravity

acting upon the moon provides the centripetal

force required for circular motion.

No centripetal force example from physicsclassroom.com

Without a centripetal force, an object in motion continues along a straight-line path.

With a centripetal force, an object in motion will be accelerated and change its direction.

Weightlessness