Gravity is a pulling force

It pulls things down towards the earth

Things fall because of gravity

Gravity holds everything and every one on the

earth

In Space, Gravity keeps the planets moving around the

sun

Aristotle

-born in 384 B.C. in Macedonia Greece. He completed his education in Athens where he spent twenty years as a student.

- “The Philosopher”.

The results of the study of motion by Aristotle are summarized as follows:

1.The fall of a heavy object toward the center of the earth is a natural motion.

2.Heavy objects fall faster than lighter ones.

3.Objects fall faster in air than in water.

Galileo Galilei (1564-1642)• he used the

telescope to make ground breaking discoveries about the Solar System

Nature of Gravity•Gravity is a force, producing acceleration•On the surface of the Earth, the acceleration due

to gravity is 9.8 meters per second per second

Time

(seconds)

Velocity

(m/s)

Accel.

(m/s2)

0 0 9.81 9.8 9.82 19.6 9.83 29.4 9.8

• His careful measurements showed that the constant acceleration due to gravity is equal to 9.8 m/s2.

Sample problems:

1.A ball is dropped from rest by a little boy from the window of a three story apartment. How far has it fallen after 1 s? What is the ball’s velocity after 1 s of fall? How far does the ball fall after 2 s?

2. The time a male bungee jumper is freely falling is 1.5 seconds.

a. What is the velocity of the jumper at the end of 1.5 seconds?

b. How far does he fall?

3. A juggler tosses three balls alternately vertically upward. Each ball has an initial velocity of 5 m/s. How high does each ball rise? How long does each ball remain in the air?

4. Vincent drops a stone from a bridge 25 m above the water. With what velocity does it hit the water?

5. A brick falls freely from a high scaffold and hits the ground after 3.5 seconds.

How high is the scaffold? What is the velocity of the brick just before hitting the ground?

6. A body is dropped from rest

and falls freely. Determine the

position and the velocity of the body

after 2.00 s have elapsed.