# Exploring Gravity and Centripetal Force

Aim: How do we describe gravity?

Do Now. p 79-81 Science Journal and Discussion: What is Projectile motion? Explain what is meant by horizontal and vertical motions. Discuss centripetal acceleration and give example. What is Centripetal force and traction. Give an example.  How can gravity be a centripetal force?

(powepoint or lab activity)

Lab: Observing Centripetal Force.p81(text)

Purpose: to observe the effect of centripetal force

Materials: string; plastic, slotted golf ball

Procedure:

1. Thread a string about 1m long through the holes of a plastic, slotted golfball.

2. Swing the ball in a vertical circle.

3. Swing the ball at different speeds and observe the motion of the ball and the tension in the string.

Analysis:

1. What force does the string exert on the ball when the ball is at the top, sides, and bottom of the swing?

centripetal force

2. How does the tension in the string depend on the speed of the ball?

the faster the ball swings, the  more tension there is on the string.

(From p82 or other image, show students a picture of a satellite in orbit. Ask them to explain how centripetal foce acts on the satellite. The centripetal force of Earth’s gravity pulls the satellit toward Earth. )

Notes:

1. gravity is an attractive force between any two objects with mass.

The gravitiational force depends on the masses of objects and the distance between tem.

2.the gravitational acceleration, g, near Earth’s surface equals 9.8m/s2.

The force of gravity on an object with mass, m, is F=mg

3.The weight of an object near Earth’s surface is w=mg

4. Projectiles travel in a curved path because of their horizontal motion and vertical acceleration due to gravity

5. The centripetal force is the net force on an object in circular motion and is directed toward the center of the circular path

Summary :(if time permits, show students several photographs of falling skydivers and ask them to analyze the sky divers’ body positions and infer the order of their velocities.)

Homework : (FROM TEXT BOOK!)

p 94# 1-6

P94. #7-14 write out the questions and the answers and the letter -answer-choice.

Define vocabulary words p 94 “Using Vocabulary”

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