Free FallFree FallFree fall occurs whenever an object Free fall occurs whenever an object

is acted upon by gravity alone.is acted upon by gravity alone.

Object that is dropped…Object that is dropped…

What do you notice about the motion of What do you notice about the motion of the object?the object?– Initial speed is zeroInitial speed is zero– The speed increases as it fallsThe speed increases as it falls– The longer it falls the faster it travelsThe longer it falls the faster it travels– The object is accelerating.The object is accelerating.

Object tossed upward…Object tossed upward…

What do you notice about What do you notice about the motion of the object?the motion of the object?– On the way up its speed On the way up its speed

decreases decreases – At the top, it stops and At the top, it stops and

reverses direction.reverses direction.– The speed increases as it The speed increases as it

falls back down.falls back down.

Why does this happen?Why does this happen?

What causes things to move downward What causes things to move downward towards the Earth?towards the Earth?– Acceleration due to gravityAcceleration due to gravity– Gravity pulls objects toward the earthGravity pulls objects toward the earth– Free fall occurs whenever an object is acted Free fall occurs whenever an object is acted

upon by gravity alone.upon by gravity alone.

Why?Why?

What are the factors do you think affect how What are the factors do you think affect how fast an object will fall to the ground?fast an object will fall to the ground?

Let’s test it…Let’s test it…

What happens when two objects of different What happens when two objects of different masses dropped at the same time?masses dropped at the same time?– The objects will hit the ground at the same timeThe objects will hit the ground at the same time

Galileo & the Leaning Tower of PisaGalileo & the Leaning Tower of Pisa

In the Sixteenth Century, it was assumed In the Sixteenth Century, it was assumed that the acceleration of a falling object that the acceleration of a falling object would be proportional to its mass.would be proportional to its mass.– Example: a 10 kg object was expected to Example: a 10 kg object was expected to

accelerate ten times faster than a 1 kg object, accelerate ten times faster than a 1 kg object, according to Aristotle.according to Aristotle.

Galileo Galilei (1564-1642) came along Galileo Galilei (1564-1642) came along and put Aristotle's theories to the test. and put Aristotle's theories to the test.

Galileo’s ExperimentGalileo’s Experiment

Galileo verified his theories Galileo verified his theories through experimentation and through experimentation and careful observation. careful observation.

Galileo dropped two objects Galileo dropped two objects with unequal masses from with unequal masses from the Leaning Tower of Pisa. the Leaning Tower of Pisa.

The two objects struck the The two objects struck the ground at the same time. ground at the same time.

The Acceleration Due to GravityThe Acceleration Due to Gravity

The acceleration due toThe acceleration due to

gravity on Earth is…gravity on Earth is…aa = 9.81 m/s = 9.81 m/s²²

aa = 22 mph or 32 feet/s = 22 mph or 32 feet/s²²

The acceleration due to gravity varies with The acceleration due to gravity varies with location.location.– greater at the poles than at the equator. greater at the poles than at the equator. – greater at sea level than in higher elevations.greater at sea level than in higher elevations.

Paper and Pencil ExperimentPaper and Pencil Experiment

How are the speed of the flat paper and How are the speed of the flat paper and pencil different?pencil different?– air resistance causes the paper go slowerair resistance causes the paper go slower

What happens if the paper in a ball instead What happens if the paper in a ball instead of flat?of flat?– They hit the ground at the same time.They hit the ground at the same time.

Terminal VelocityTerminal Velocity

A free-falling object A free-falling object reaches terminal velocity reaches terminal velocity when the downward when the downward force of gravity equals force of gravity equals the upward force of air the upward force of air resistance. resistance. – 120 mph or 55 m/s120 mph or 55 m/s– Example Skydiving Example Skydiving

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