May the Force be with you

This is funny

Definition

Force:  any push or pull on an object (it's that simple)

….But be careful! Commonly students will think

forces have to come from living or moving things.  Not true.  Gravity pulls a chair to the floor and the floor pushes back.

Forces can cause:  

1) speeding up 2) slowing down 3) change in direction        IN OTHER WORDS FORCES CAN*

CAUSE: ACCELERATION*(but they don’t always cause

acceleration!)

Balanced forces:

  When all the forces cancel each other out= no net change in motion  (no acceleration!)

Unbalanced forces: 

Two or more forces that work and add together to change motion  (cause acceleration)

Example of a canoe being rowed on a river on a windy day

http://rt210.sl.psu.edu/simulations/physlets/force_table.html

Vectors

Forces are vectors Vectors are ____________with

______________ Which one is a vector: Speed

or Velocity?

Newtons

In the metric system, the unit of force is the Newton.

It can be used to quantify the pull or push of ANYTHING!

What is correct: To weigh something in pounds, Newtons, or Kilograms?

 balanced forces example: 

You on a chair  you are pulled down by gravity and

the chair pushes back on your butt.  Think about it....If you sat on the hard chair for three hours without moving, wouldn't you feel the chair's push?

unbalanced forces example: 

a rocket taking off

the force of the engines is enough to overcome gravity and the rocket accelerates off the launch pad

Questions

Is it possible to have one balanced force? If so, draw as a vector diagram.

Is it possible to have 2 balanced forces? If so, draw as a vector diagram.

Is it possible to have 3 balanced forces? If so, draw as a vector diagram.

More questions

Can an object be in motion with balanced forces acting on it? Defend your answer.

Can an object be stationary with unbalanced forces acting on it? Defend your answer.

More….

Can you predict the motion of this box?

Force: 5 N

Friction:  a force; it causes negative

acceleration (slows things down and makes them stop) (Can it also aid positive acceleration?)

it's mostly caused by: interaction of the matter that is in contact

Also caused by differences in materials that are in contact.

The Three Types of Friction and Each One’s Properties

3 types Typical Relative strength

Examples

Sliding Strongest Book pushed on table

Rolling Medium Car wheels

Fluid Lowest Swimming or flying

From mass to Force (Part II)

Mass: Amount of Matter in an object Something is hard to move if it has more mass

Basically the “amount of stuff” found in something

Inertia

Objects with mass don’t like to move

This property is inertia

How is it measured?

Weight

Weight is a ___________ Caused by ___________ All atoms are pulled by gravity, so

things with atoms have weight

Speed and Velocity

Rate of motion Velocity includes direction V= D/T (with direction) Units: Meters per second

Momentum When things move faster, they become

harder to stop And when they are more massive they

are also harder to stop Momentum is like “inertia in motion” ρ=Mass times velocity Momentum is not a force, but it takes a

force to stop momentum……… Units: Kilogram Meters per second

Acceleration

When speed or direction changes Only a force can cause acceleration Change in speed divided by time Or Ending speed – Starting speed TimeUnits: Meters per second squared

Acceleration when falling

On earth this is at a rate of 9.8 m/s/s

This is a fast rate of acceleration

What affects this acceleration during the fall?

Finally………Force

Any push or pull Forces can accelerate a mass Force equals mass times

acceleration F= MA Units: Kilogram meters per second

squared (or Newtons)

Weight is a Force On earth you calculate weight byMultiplying mass (in Kg) times

acceleration due to gravity (9.8 m/s/s)

This will give you weight in Newtons Weight= mg If you wanna turn your mass into

weight….don’t forget to multiply by 9.8 (m/s/s)