SECTION 2 (PART 1) – Gravity

LEARNING GOALS Describe gravitational force. Distinguish between mass and

weight.

GRAVITY Gravity: an attractive force

between any two objects Depends on the masses of the

objects and the distance between them

GRAVITY

You

Your book is closeenough to exert aforce you can feel but it is too small. Jupiter is large

enough to exert a noticeable force, but its too far away.

The Earth is large enough andclose enough to exert a noticeableforce.

THE LAW OF UNIVERSAL GRAVITATION Newton’s equation enables the force of

gravity to be calculated between any two objects if their masses and the distance between them is known.G = universal gravitation

constantm1 = mass of the 1st objectm2 = mass of the 2nd objectd = distance between the two masses

THE LAW OF UNIVERSAL GRAVITATION As the distance between two

objects increases, the gravitational force between them decreases.

No matter how far apart two objects are, the gravitational force never completely goes to zero!

THE EARTH’S GRAVITATIONAL ACCELERATION Close to the Earth’s surface, the

acceleration of an object in free fall is 9.8 m/s2. Free fall ignores all forces except

gravity!

This acceleration constant is sometimes labeled g.

THE EARTH’S GRAVITATIONAL ACCELERATION Using Newton’s 2nd Law of

Motion, the force of Earth’s gravity on a falling object isF = force of gravity on a falling

object (N)

m = mass of the object (kg)

g = gravitational acceleration constant

(9.8 m/s2)

F = mg

FORMULA SHEET

F = mgm = F/gg = F/m

EXAMPLE What is the gravitational force

on a sky diver with a mass of 600 kg?

WEIGHT Even if you aren’t falling, the force of

Earth’s gravity is still pulling you downward.

Weight: the gravitational force exerted on an object

Weight can be calculated by the following equation: W =

mg

FORMULA SHEET

W = mgm = W/gg = W/m

WEIGHT AND MASS Weight and mass ARE NOT THE

SAME THING! Weight is a measure of force, mass is

the measure of the amount of matter in an object.

Weight changes as gravity changes; mass does not.

EXAMPLE A person on Earth has a mass of

54 kg, what is their weight?