Describing Motion. Basic Terminology Position: Where an object is located in space Think of mile markers along a highway.

Describing Motion

Basic Terminology

Position: Where an object is located in space

Think of mile markers along a highway

Basic Terminology

Position: Where an object is located in space

Think of mile markers along a highway

Speed: How quickly position is changing – just a non-negative number

Velocity: How quickly position is changing – includes direction of change

Basic Terminology

Position: Where an object is located in space

Think of mile markers along a highway

Speed: How quickly position is changing – just a non-negative number

Velocity: How quickly position is changing – includes direction of change

Acceleration: How quickly velocity is changing – includes direction of change

Any change in velocity is an acceleration

Turning is acceleration:

While speed may be constant, the direction of the velocity is changing

How many “accelerators” – in the physics sense of the word – does a car have?

A) 1: The gas pedal

B) 2: The gas pedal and the brake

C) 3: The gas pedal, the brake, and the steering wheel

D) 4: The gas pedal, the brake, the steering wheel, and the blinkers

Acceleration: How quickly velocity is changing – includes direction of change

Can include speeding up, slowing down, OR turning

Acceleration due to gravity

Every second in freefall, the force of gravity adds 10 m/s to the speed of the falling object

We say the object’s acceleration isg = 10 m/s/s = 10 m/s2

NOTE: This is the value at the surface of the Earth

(more precisely, g = 9.8 m/s2)

Of course, this ignores air resistance…

Air resistance demo…

Ignoring air resistance, how fast will a rock be falling 5 seconds after it is dropped?

A) 5 m/s

B) 10 m/s

C) 25 m/s

D) 50 m/s

E) 100 m/s

Force and Momentum

Momentum is the product of mass and velocity

The faster an object moves, the more momentum it has.

A more massive object, traveling at the same speed, will have more momentum.

Demonstration . . .

Force and Momentum

Momentum is the product of mass and velocity

The faster an object moves, the more momentum it has.

A more massive object, traveling at the same speed, will have more momentum.

Demonstration . . .

The only way to change on objects momentum is to apply a Force to it.

Conversely, if a net force is applied to an object, the object’s momentum WILL change.

Demonstration . . .

Force and Momentum

Momentum is the product of mass and velocity

The faster an object moves, the more momentum it has.

A more massive object, traveling at the same speed, will have more momentum.

Demonstration . . .

The only way to change on objects momentum is to apply a Force to it.

Conversely, if a net force is applied to an object, the object’s momentum WILL change.

Demonstration . . .

Momentum of an object is “conserved” if there are no external forces.

Rotational Motion

An object that is rotating has Angular Momentum

Demonstration . . .

Mass and Weight

Mass is the amount of matter in an object.

Weight is the force that a scale measures when you stand on it.

Weight depends on mass as well as gravity and other forces acting on an object…

Mass and Weight

Mass is the amount of matter in an object.

Weight is the force that a scale measures when you stand on it.

Weight depends on mass as well as gravity and other forces acting on an object…

Mass and Weight

Another example…

If Buzz Aldrin weighed 190 lbs on Earth, he only weighed 31 lbs on the Moon.

His mass didn’t change.

“Weightlessness”

In freefall, there IS gravity.Man and machine fall together, accelerating at the same rate.

So neither has to push on the other – they’re “weightless”

Astro-Cash Cab!

Carl Cook

Quincey Davison

Rebecca Lopez

Faleen Lobato

Jeffrey Crawford

1) What do we call any change in motion?

A) Force

B) Mass

C) Speed

D) Velocity

E) Acceleration

2) True or False ?

Astronauts in space are weightless because there is no gravity in space.

3) Which of the following is NOT an example of acceleration?

A race car driving at 225 mph on a long straightaway.

A kid on a bicycle going 5 mph around a turn.

A book sliding to a stop on the floor.

A spacecraft in orbit around the Earth.

4) Compared to standing on earth, when an astronaut is standing on the Moon her _________ is the same, but her _________ is different.

Mass

Weight