Answer these questions…

1. Why doesn’t earth fly off into space?

2. Where is Gondwanaland?

3. How do airplanes stay in the sky?

4. How much do you weigh in a pool of water?

Notes: Speed, Velocity and Acceleration

How do you know if an object is in motion?

• It’s distance from another object is changing• The other object is the reference point ( a place

or object used for comparison to see if an object is moving)

How do you describe motion?

• Distance – How far it goes (measured in meters)

• Speed – How fast it goes

• Time – How long it takes to get there

• Formula for Speed = Distance/Time

• Example: 50 miles per hour

Constant Speed

• Constant Speed – When an object’s speed is the same at all times during it’s motion– Example – an ship traveling across the ocean

may move at the same speed for several hours

– Long Distance Swimmers/Runners – keep the same pace for a certain part of the race

– Practice Problem: A train travels at a constant speed of 80 miles in 2 hours. What is it’s speed?

Average Speed

• Most objects do not move at the same speed for the entire time that it is in motion.– Example: A cyclist may glide over level

ground, climb slowly up a hill, speed down hills

– Practice Problem: A car is driven 60 miles in 2 hours and 100 miles during 4 hours. What is the car’s average speed?

Velocity

• Speed in a given direction

• Example – 4 meters per second North

• Who would use velocity in their careers?

• How would they use velocity?

Theory of Plate Tectonics

• Earth’s plates move in various directions very slowly

• Pangaea – super continent

• Laurasia – Northern mass of super continent

• Gondwanaland – Southern mass of super continent

http://pubs.usgs.gov/publications/text/historical.html

http://library.advanced.org/17701/high/pangaea/

Figure this one out…

• Suppose scientists discover that a plate will move 5 centimeters per year.

• Can you predict how far the plate will move in 1,000 years?

• How far will the plate move in a day?

Alfred Wegener (1880-1930) Developed Theory of Pangaea

Alexander du Toit (1878-1948) Believed that Pangaea broke apart into 2 super-continents – Laurasia and Gondwanaland

Acceleration• A change in

velocity -either increasing speed, decreasing speed or changing direction

• Acceleration =

• (Final Velocity – Initial Velocity)/Time

Figure this one out…

• A roller coaster picks up speed as it rolls down a slope.

• As it starts down the slope it’s speed is 4 meters/second, but 3 seconds later it’s speed is 22 meters/second.

• What is the average acceleration?

Explain This…

• When you travel in a car, where do the pushes and pulls you feel come from?

• When you experience pushes/pulls associated with acceleration, you continue the motion you had BEFORE the acceleration began.

• Check out the go-kart picture

To Make Motion Graphs Easier:

1. A straight line means constant speed.

2. A horizontal line means no motion, 0 speed.

3. A positively sloped line means motion away from the reference point, + velocity

4. A negatively sloped line means motion toward the reference point, - velocity

5. A steeper slope = faster speed.

To Make Motion Graphs Easier:

6. The value of the slope is defined by the graphed units of time and distance

7. A curved line means a change in speed.

8. The rate of curvature defines the amount of acceleration.

Demonstration

• What affects the acceleration of an object?

• Which student moves faster?

• Which student moves further?

• Which student stays in place?

Why did this happen?

• Objects with a larger mass have a greater resistance to acceleration.

• Inertia – the tendency of an object to resist changes in motion

• Force – a push or pull (sometimes results in motion)

Demonstration – Penny Activity

• What will happen to the penny if you YANK the card out from under it?

Yikes!!! Help Me!!

Why did this happen?

• What actually happened? You caused the card to accelerate horizontally.

• Why did this happen? The force was applied to the card only – Inertia kept the coin from moving.

• Do you think it would be different if you pulled it slowly? It should go with the card everytime.

Who is Isaac Newton?

• An English mathematician that discovered the three laws of motion.

Newton’s First Law

• An object remains in motion or at rest unless acted on by a force

Balanced vs. Unbalanced Force

• Balanced Forces – all the forces acting on an object cancel each other out

• Unbalanced Forces – when there is a greater force in some direction causes movement

Friction

• A force that resists motion between two objects in motion that are touching

• Example – a runner’s shoes and the running surface

• Ice – not enough friction

• Mud – too much friction

• Example – air hockey table

There are three types of friction

Sliding Friction

• When two objects are rubbing against each other

Rolling Friction

• The friction that exists when a wheel turns on a surface.

• Caused by the small indentations created as one surface rolls over another

• Resists slipping and spinning

Fluid Friction

• The friction on a solid object as it moves through a liquid or gas

Gravity

• A force that pulls free falling objects to earth’s center

• All objects accelerate downward at a rate of 9.8 m/s2 (meters/second squared)

Demonstration – Money, Money

• Do all objects fall at the same rate?

• Which would fall faster a book or a dollar bill?

• Why?

• How can we get them to fall at the same rate?

Why did this happen?

• As objects fall, more massive objects are more attracted to the earth but are also harder to accelerate (because of inertia)

• Their inertia reduces their acceleration by exactly half as much as their greater attraction increases it

What is the difference between mass and weight?

• Mass – the amount of matter in an object

• Greater mass = greater inertia

• So mass= the amount of inertia in an object

• Weight – the gravitational pull of an object toward the earth

Overhead 6

Newton’s 2nd and 3rd Law

Newton’s Second Law

• The force of an object is equal to the product (think math – what is a product) of its acceleration and its mass

• Force = Mass x Acceleration

• Force is Measured in Newtons

• Mass – usually in Kg

• Acceleration = m/s2

Think about it…

• Since weight is a force you can rewrite Newton’s second law:

• Weight = mass x acceleration

Newton’s Third Law

• For every action force there is an equal and opposite reaction force.

Action vs. Reaction Force

• Action Force – a push on something

• Reaction Force - the force that pushes back

• Example – balloon, fire hose, bullet fire, passing gas in the bath tub

Newton’s Third Law Cont.

• How many objects is Newton talking about in his third law?

• Can Action and Reaction forces be added together?

• No• Why or Why not? Because they are acting

on different objects

Examples

• Figure Skaters – one skater pushes against the other – both move

• Squid – pushes water out - he moves forward

BUT….

• Remember the roller chairs….

• Who moved further?

• Speed and amount of movement when 2 objects are in contact depends on mass.

Another Example

• If forces are equal in strength but in opposite directions then they cancel each other out.