Forces and Motion…Forces and Motion…

Everyday pushes and pullsEveryday pushes and pulls

(that we never think about)(that we never think about)

Everyday ForcesEveryday Forces

Forces

Gravitation Magnetism Friction

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

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

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

Balanced forces are equal in size and opposite in Balanced forces are equal in size and opposite in direction.direction.

When forces are balanced, no change in motion occurs.

Unbalanced forces are NOT equal in size and

Unbalanced forces are NOT equal in size and

opposite in direction.

opposite in direction.

When forces are unbalanced, a change in motion occurs.

How can I tell when motion is occurring???How can I tell when motion is occurring???I need to know an objectI need to know an object’s starting ’s starting positionposition to be to be

able to tell it has moved over a distance!able to tell it has moved over a distance!

Distance

Speed: How long it takes to travel a given Speed: How long it takes to travel a given distancedistance

Formula: Distance/Time = SpeedFormula: Distance/Time = Speed Ex: 55 miles/1 hour = 55 miles per hourEx: 55 miles/1 hour = 55 miles per hour

Distance = 55 miles

Time = 1 hour

Graphing Speed:Graphing Speed:Distance vs. Time GraphDistance vs. Time Graph

Phoenix

Denver

Question:Question:Below is a distance vs. time graph for 3 Below is a distance vs. time graph for 3

runners. Who is the fastest?runners. Who is the fastest?

Leroy is the fastest. He completed the race in 3 hours.

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

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

Example: Example: An airplane moving North at 500 mphAn airplane moving North at 500 mphA missile moving towards you at 200 m/sA missile moving towards you at 200 m/s

Question:Question:

What is the difference between speed and velocity?

Speed is just distance/time. Velocity includes direction as well.

The rate at which velocity changes is calledThe rate at which velocity changes is calledaccelerationacceleration..It can be: •an increase in speed•a decrease in speed•a change in direction

Question:Question:

How can a car be accelerating if its speed is a constant 65 km/h?

If it is changing directions it is accelerating

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

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

Ex: Ex: ItIt’s harder to stop a 200 lb. ’s harder to stop a 200 lb. linebacker than a 100 lb. linebacker than a 100 lb. ballerinaballerina

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.