Force Mass

Motion

How can I get the catapult to hit the

target the first time?

Aristotle’s View

Two types of motion:

Natural motion - what an object “naturally wants to do”

Violent motion - what an object has to be forced to do

Aristotle’s View

In order for a “normal” object to move at constant velocity, something must be pushing on it. When the pushing stops, the object (perhaps gradually) comes to a stop.

Galileo’s View

Realized that the classical view of motion did not recognize the role of friction

If left to themselves, moving objects don’t slow down.

Newton’s First Law

Whatever an object is doing, that’s what it wants to keep doing.

If left to themselves, objects will keep doing whatever they’re doing.

Newton’s First Law

Objects at rest tend to stay at rest.

Objects in motion tend to stay in motion.

Newton’s First Law

If there is no net force on an object, the object won’t accelerate.

Acceleration is not the same as motion…it is a change in motion!

Newton’s First Law

The converse is also true:

If an object is not accelerating, then there is no net force on it.

What is an “object”?

Anything made of matter is an “object”.

What is a “force”?

A force is an interaction between 2 objects involving a push or a pull.

Forces are vectors - they have a direction in space.

Common units of force are: pounds, Newtons, or dynes.

What is a “net force”?

The net force on an object is the vector sum of all of the forces that push or pull on the object.

Adding vectors

“no net force on an object” means:

either there are no forces on the object, or:

the forces that push or pull on the object all cancel exactly.

“object won’t accelerate” means:

the object:

–won’t speed up.

–won’t slow down.

–won’t change direction.

Newton’s First Law can be stated:

If no forces push or pull on an object, or if the forces that do push or pull on it all cancel exactly, then the object will not speed up, slow down, or change direction.

Inertia

In other words…

Objects tend to remain at rest until you hit them

AND

Things keep on doing whatever they are doing until something else hits them.

Inertia

Newton’s First Law says that objects do not accelerate spontaneously.

This property of matter, which causes objects to resist acceleration, has been named “inertia”. Coin & cup…

Newton’s First Law is often called the Law of Inertia.

Friction

Friction is a force that arises due to the relative motion of two surfaces.– Two solid surfaces - sliding friction, rolling

friction– A solid and a fluid - air resistance– Two fluids– Paper and book…

Friction

The direction of the friction force always opposes the relative motion of the surfaces.

Friction

The amount of sliding friction depends on:– The condition (smoothness/roughness) of

the surfaces

Newton’s Second Law

Force is proportional to mass

F = ma dropping balls…

Newton’s second law

Gravity is constant for all falling objects

The force of the fall depends on massMythBusters Link-  dropped bullet vs. a fired bullet http://dsc.discovery.com/videos/mythbusters-simultaneous-bullet-release.html

Indian and the Canoe

http://library.thinkquest.org/3042/java/linear_demo.html 

*Answer questions and complete table on handout.

Newton’s third law

For every action there is an equal and opposite reaction

Momentum is conserved

If time check out…

Roller coaster Physics: It is your mission to design the coaster so that you can achieve maximum thrills and chills without crashing or flying off the track (unless that 痴 how you like your coaster to work!).If you accept this mission you must decide on a number of factors. You are responsible for setting the controls for the height of hill #1, hill #2, the size of the loop, the initial speed of the coaster, its mass, the gravity at work and the amount of friction on the track. 

http://www.funderstanding.com/coaster 

OR

Momentum: http://www.glencoe.com/sites/common_assets/science/virtual_labs/E24/E24.html