Forces in Motion

What Do You Think?

How does the force of gravity affect falling

objects?

Forces in Motion

Gravity causes all objects to fall toward the ground with the same acceleration, 9.8 m/s2.

http://mired.org/home/mwm/parachuting/floating2.jpeg

Forces in Motion

A little vocabulary before we start…

• Force- a push or a pull• Velocity- the speed of an object

and its direction of motion.• Acceleration- the rate at which

the velocity changes.

Forces in Motion

Activity

Drop a tennis ball and a golf ball from a table at the same height at the same time.

Which hits the ground first?

Forces in Motion

• In the late 1500s, Galileo found that mass does not affect the time the object takes to fall to the ground.

• Both the elephant and the feather hit the ground at the same time.

• This only happens if there is NO air resistance.

http://www.physicsclassroom.com/mmedia/newtlaws/efff.html

Forces in Motion

Air resistance is a fluid friction that opposes the motion of object through the air.

It slows down acceleration.

Forces in Motion

Drop 2 sheets of paper- one crumpled in a tight ball and the other kept flat.

What happens? Why?

Forces in Motion

Air resistance is affected by:

• The Size of the object

• The Shape of the object

• The Velocity of the object

Forces in Motion

This is what happens to the elephant and feather when air resistance is present.

http://www.physicsclassroom.com/mmedia/newtlaws/efarm.htl

Forces in Motion

An object is in free fall only if gravity is pulling it down and no other forces are acting on it.

Forces in Motion

• Because air resistance is a force, free fall can only occur where there is no air, such as a vacuum (a place in which there is no matter) or in space.

• If the feather and the elephant were in free fall, they would hit the ground at the same time.

Forces in Motion

• Astronauts appear to be “weightless” in space because of free fall.

• Both the astronaut and the space shuttle are falling toward the earth at the same rate.

Forces in Motion

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How an orbit is formed

Forces in Motion

Projectile Motion is the curved path an object follows when it is thrown or propelled near the surface of the Earth.

Forces in Motion

Projectile motion has 2 components: horizontal and vertical.- When throwing a ball, horizontal motion occurs when the ball leaves your hand.- After the ball leaves your hand, gravity pulls it down giving it vertical motion.

Forces in MotionProjectile Motion from a Baseball

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