Forces and Motion…

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# Forces and Motion… - PowerPoint PPT Presentation

Forces and Motion…. Everyday pushes and pulls (that we never think about). Everyday Forces. Which two forces have we studied this year?. 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….

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Presentation Transcript

### Forces and Motion…

Everyday pushes and pulls

Everyday Forces

Which two forces have we studied this year?

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…

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

Friction keeps us from sliding off the skateboard.

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 direction.

When forces are balanced, no change in motion occurs.

When forces are unbalanced, a change in motion occurs.

How can I tell when motion is occurring???

Distance

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

Speed: How long it takes to travel a given distance

Time = 1 hour

Distance = 55 miles

Formula: Distance/Time = Speed

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

Question:Below is a distance vs. time graph for 3 runners. Who is the fastest?

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

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
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 calledacceleration.
• It can be:
• an increase in speed
• a decrease in speed
• a change in direction

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

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.

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.

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