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Aristotle

He thought that the rate at which an object falls depended on the object's mass.

Galileo

He argued that the mass of an object does not affect the time the object takes to fall to the ground.

Objects fall to the ground at the same rate

because the acceleration due to gravity is the same for all objects.

Acceleration depends on

both force and mass

Acceleration

this is the rate at which velocity changes over time.

All objects accelerate towards Earth at a rate of

9.8 meters per second per second.

9.8 m/s/s/

This means 9.8 meters per second per second.

In the second second an object falls, the downward velocity is

19.6 m/s downward

In the third second an object falls, the downward velocity is

29.4 n/s downward

In the first second an object falls, the downward velocity is

9.8 m/s downward

The equation for change in velocity is

∆v = g × t

In ∆v = g × t, the g stands for

acceleration due to gravity on earth

In ∆v = g × t, the t stands for

the time the object takes to fall.

29.4 m/s

The speed of an object when it hits the ground after a period of 3 seconds.

19.6 m/s

The speed of an object when it hits the ground after a period of 2 seconds.

If an object hits the ground with a velocity of 98 m/s, how long did it take to reach the ground

10 seconds.

If an object hits the ground with a velocity of 49 m/s, how long did it take to reach the ground

5 seconds

air resistance

force that opposes the motion of objects that move through the air

the force of gravity

this pulls down on a falling object

this force pushes up on a falling object

air resistance

net force on a falling object

the force of air resistance subtracted from the force of gravity.

free fall

This occurs only if gravity is pulling down an object with no other forces acting on it. It is usually accompanied by the playing of a Tom Petty song. :)

free fall only occurs where there is

no air

two places there is no air

space and a vacuum. A third place is also potentially inside an 8th graders brain. :)

weight

this is a measure of gravitational force.

terminal velocity

the constant velocity of a falling object when the force of air resistance is equal in magnitude and opposite in direction to the force of gravity

why is terminal velocity a good thing

because if there was no maximum speed, things like hailstones would destroy everything in their path.

parachute

this increases air resistance and slows one to a safe terminal velocity.

It is impossible for

any object to be weightless anywhere in the universe.

orbiting

when an object moves in a regular path around another object

centripetal force

any force that causes an object to move in a circular path

centripetal means

towards the center

Why does the moon stay in orbit

because the Earth's gravitational force provides a centripetal force on it.

projectile motion

the curved path that an object follows when thrown, launched, or otherwise projected near the surface of Earth

hopping grasshopper

The motion of this activity is an example of projectile motion.

leaping frog, water sprayed by a sprinkler, an arrow shot by an archer

These are all examples of projection motion.

horizontal motion

motion that is parallel to the ground

which two forces combine to cause projectile motion

horizontal motion and vertical motion.

vertical motion

motion which is perpendicular to the ground.

a ball dropped without a horizontal push wll

fall straight to the ground

a ball which is given a horizontal push will

fall to the ground with projectile motion

Does gravity affect horizontal motion?

No, it only affects vertical motion.

If a rock at rest falls off a tall cliff and hits the valley below after 3.5 s, what is the rock's velocity when it hits the ground?

34.3 m/s downward

Newton's First Law of Motion

Objects in motion will remain in motion unless acted upon by another force.

unbalanced force

This is what changes the velocity of an object as defined in Newton's First Law.

unbalanced force that acts upon something pushed on the floor to stop it

friction

Objects at rest

tend to stay at rest until an unbalanced force acts upon it.

law of inertia

The other name for Newton's First Law of Motion

inertia

the tendency of an object to resist being moved or, if the object is moving, to resist a change in speed or direction until an outside force acts on the object.

Newton's Second Law of Motion

The acceleration of an object depends on the mass of the object and the amount of force applied.

Newton's Second Law of Motion: Part 1

Acceleration Depends On Mass

Newton's Second Law of Motion: Part 2

Acceleration Depends On Force

Why do newer cars pollute less than older cars?

They have less mass, so it requires less force to move them.

Acceleration will increase when

a larger force is exerted.

F = m × a

The correct formula for Newton's second law of motion.

Newton's second law explains why objects fall to Earth

with the same acceleration.

What is the acceleration of a 3 kg mass if a force of 15 N is used to move the mass? Note: 1 N = 1 kg×m/s

5 m/s

What is the acceleration of a 4 kg mass if a force of 16 N is used to move the mass? Note: 1 N = 1 kg×m/s

4 m/s

What is the acceleration of a 3 kg mass if a force of 18 N is used to move the mass? Note: 1 N = 1 kg×m/s

6 m/s

What is the acceleration of a 2 kg mass if a force of 18 N is used to move the mass? Note: 1 N = 1 kg×m/s

9 m/s

Newton's Third Law of Motion

Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first.

Swimmer action force

Hands pushing through the water.

Swimmer reaction force

Water pushing on the hands.

For a swimmer, which force pushes them forward

The reaction force.

A force is always exerted by one object

on another object.

Action and reaction forces are a

pair of forces

Space shuttle action and reaction force pairs

Thrusters pushing the exhaust games downward as gases push the shuttle upward with equal force.

Action and reaction forces example

A rabbit's legs exerting a force of Earth with Earth exerting an equal force on the rabbit's legs causing the rabbit to accelerate forward.

Equal and opposite force

whenever an object exerts a force on another object, the second object exerts this...

momentum

a quantity defined as the product of the mass and velocity of an object.

formula for momentum

p = m × v

What is the momentum of a ball with a mass of 120 kg that moves with a velocity of 16 m/s?

19,200 kg m/s

What is the momentum of a ball with a mass of 100 kg that moves with a velocity of 16 m/s?

16,000 kg m/s

What is the momentum of a ball with a mass of 200 kg that moves with a velocity of 16 m/s?

32,000 kg m/s

What is the momentum of a ball with a mass of 200 kg that moves with a velocity of 12 m/s?

24,000 kg m/s

What is the momentum of a ball with a mass of 100 kg that moves with a velocity of 12 m/s?

12,000 kg m/s

What is the momentum of a ball with a mass of 150 kg that moves with a velocity of 12 m/s?

18,000 kg m/s

law of conservation of momentum

this means that anytime objects collide, the total amount of momentum stays the same.

when does the law of conservation of momentum apply

then objects stick together or bounce off each other after they collide.

billiard balls bouncing off one another

This is an example of the law of conservation of momentum

The more momentum an object has.....

the harder it is to stop the object or change its' direction.

If a truck has more mass than a car....

a larger force is needed to stop the truck than the car.

If a fast moving car has a greater velocity than a slow moving car....

a larger force is needed to stop the faster moving car.

Objects sticking together

After this happens, they move as one. the masses of the objects remain the same. The velocity changes. total momentum before and after collision stays the same.

Objects sticking together - examples

When one football player tackles another player or when a dog catches a ball.

Objects bouncing off one another - examples

Bowling balls and pins, billiard balls

Objects bouncing off one another - what is happening

Momentum is transferred from one object to another object.

Objects sticking together - what is happening

The mass of the combined object is equal to the mass of the two objects added together. Together, the one object has a velocity which is different from the velocity of the two individual items.

Conservation of momentum is explained by

Newton's 3rd Law of Motion

When a cue ball hits a billiard ball.......

the cue ball creates the action force, which makes the billiard ball move.

What is the reaction force when a cue ball hits a billiard ball.......

this is the equal but opposite force exerted by the billiard ball on the cue ball. It make the cue ball stop moving.

Momentum is a property of....

moving objects.