Forces and Motion

Everyday Forces

Forces

GravitationMagnetism Friction

Which forces have we studied this year?

Forces

Force 1. Earth and everything on it are affected by FORCES.

2. A force is a PUSH OR A PULL that causes an object to move, STOP, change direction, SPEED up, or slow down. It is measured in units called NEWTONS (N) after Sir Isaac Newton.

3.There are three forces on Earth every day that affect motion: friction, MAGNETISM, and gravity.

Look closely at each

picture. What would you

do with it: push or pull?

Gravity: the pull between all objects (the greater the mass, the harder the pull!!!)

Discovered by Sir Isaac Newton when an apple fell upon his head…

GravityGravity affects objects on Earth all the time.

·It hold things to the SURFACE of the Earth.

·It pulls objects (big or small) TOWARDS each other.

·Gravity is WEAKER between smaller objects and larger for objects of greater mass.

·The CLOSER objects are to each other, the greater the force of gravity.

Friction: causes motion to slow down or stop… causes drag!

Friction keeps us from sliding off the skateboard.

The rough surface of the mountain causes friction and gives us a grip on the side of the mountain when we rock climb.

The tread on our shoes causes friction, and keeps us from ending up like this guy on icy roads.

Friction  Friction opposes or acts AGAINST motion. · It occurs when two objects RUB against each other. · The harder the surfaces press together, the MORE friction there will be.· Friction occurs in LIQUIDS and GASES as well as between solids.· Without friction , it would be difficult to SLOW or stop the motion of objects.

Balanced forces are equal in size and opposite in direction.

When forces are balanced, no change in motion occurs.

Unbalanced forces are NOT equal

in size and opposite in direction.

When forces are unbalanced, a change in motion occurs.

When the net force is Zero.-> NO movement

When the net force is NOT Zero.-> movement

When the net force is Zero.-> NO movement

When the net force is NOT Zero.-> movement

How can I tell when motion is occurring???

I need to know an object’s starting position to be able to tell it has moved over a distance!

Distance

Speed: How long it takes to travel a given distance

Formula: Distance/Time = Speed

Ex: 55 miles/1 hour = 55 miles per hour

Distance = 55 miles

Time = 1 hour

Average Speed = distancetime

Graphing Speed:Distance vs. Time Graph

Phoenix

Denver

How fast something looks like it’s moving all depends on your frame of reference .

Velocity: The speed of an object in a particular direction.

Example: An airplane moving North at 500 mph A missile moving towards you at 200 m/s

The rate at which velocity changes is calledacceleration.

When an object’s motion changes by slowing down, we call this deceleration.

It can be: • an increase in

speed• a decrease in

speed• a change in

direction

Momentum: How hard it is to start or stop an object.

*The more mass an object has, the more momentum it has.

Ex: It’s harder to stop a 200 lb. linebacker than a 100 lb. ballerina

The faster an object is moving, the more momentum it has.Ex: It’s harder to stop a car going 50 miles an hour than a car going 10 miles an hour.

Newton's law

Newton’s Laws of Motion

Law #1: Law of InertiaLaw #2 : F= m x aLaw #3 : Action / Reaction

Law #1: Law of Inertia

An object at rest will remain at rest unless acted on by an unbalanced force.

An object in motion continues in motion with the same speed and in the same unbalanced force.

This law is often called “the law of inertia”

Law #2: F= m x a

Acceleration is produced when a force acts on a mass.

The greater the mass (of the object being accelerated ) the greater the amount of force needed (to accelerate the object)

This means that heavier objects require more force to move the same distance as lighter objects.

* The second law gives us an exact

relationship between force , mass

and acceleration. It can be

expressed as a mathematical

equation:

F= m x a

Force = mass x acceleration

Law #3: Action / Reaction

For every action there

is an equal and

opposite re-action.

3rd law of Newton This law means that for every force there is a

reation force that is equal in size, but opposite in

direction. That is to say that whenever an object

pushes another object it gets pushed back in the

opposite direction equally hard.