1. Motion
Chapter 2
Sections 1-3

2. Motion Section 1 - Describing Motion slides 3- 21
Section 2 - Acceleration slides 22 – 28
Section 3 – Motion & Forces slides

3. Section 1- Describing Motion
What You’ll Learn:
The difference between displacement & distance
The difference between speed & velocity
How to graph motion

4. Motion
Distance & time are important in describing a race. The winner covers the distance in the shortest amount of time.
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5. How are motion & position related?
A reference point is needed to tell where something is or if it has moved.
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6. What is relative motion?
Not all motion is obvious. When you are sitting still, you appear not to be moving although you are moving in relation to the Sun because you are sitting on Earth.
Relative motion means that one thing moves in relation to another thing. Earth is moving in space in relation to the Sun. The Sun is the reference point for the Earth’s motion.

7. How are distance & displacement different?
Distance is how far something has moved. The distance of a 50 m dash is 50 meters.
Displacement is the distance & direction of an object’s position relative to the starting point.
Running of the Bulls (Pamplona, Spain)
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8. Speed
To tell how fast something is moving, you need to know how far it travels in a certain amount of time.
Speed is the distance an object travels per unit of time.
“Hundreds of people and six fighting bulls, accompanied by steer, sprinted the half-mile (850-meter) route through cobblestone streets in just over two minutes…” Associated Press
Speed = 850m / 2 min= _______ m/s

9. How is speed calculated?
Speed = distance/time= m/s
850m/ 2 min or 120 sec= 7.08 m/s
We divide the distance traveled by the time it took to travel the distance.
“Hundreds of people and six fighting bulls, accompanied by steer, sprinted the half-mile (850-meter) route through cobblestone streets in just over two minutes…” Associated Press
Speed = 850m / 2 min= _______ m/s

10. What is motion with constant speed?
A speedometer measures the speed of a car. Suppose you look at it when you are riding on a freeway. The car is not speeding up or slowing down; it is moving at a constant speed.
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11. What is changing speed? 25 20 Usually speed is not constant. 15
Here we see how the speed of a cyclist changes over 5 km.
The ride took 15 minutes.
Speed Changing Over Distance 25 20 15 10 5
Going downhill
Stopping for red light
Speed (km/hr)
Climbing steep hill
Constant speed
Gaining speed
Distance

12. What is average speed?
Average speed is the total distance traveled divided by the total time of travel.
It is calculated using the relationships among speed, distance & time.
Average speed= total distance / total time= 5 km/15 min or .25 hr= 20 km/hr.

13. What is instantaneous speed?
Instantaneous speed is the speed at one point in time, or one instant.
If an object moves with constant speed, the speed remains the same; however, if it speeds up or slows down, the instantaneous speed is changing.

14. Graphing Motion
A distance- time graph shows the motion of an object over time.

15. Graphing Motion The steepness of the line is its slope (m).
The slope of the line is the speed. A steeper slope means a greater speed.
Slope= rise/run or ∆y/∆x
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16. How is changing speed graphed?
The changing slope in this graph indicates changing speed.
Review graphing from Chapter 1 notes.
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17. How do you draw a distance-time graph?
Distance is plotted on the vertical (y) axis & time is plotted on the horizontal (x) axis.
Each axis has a scale, or series of numbers, that covers the range of the data.
Each axis is divided into equal parts; then the data points are plotted on the graph and finally connected with a line.
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18. Velocity
Suppose there is a storm nearby traveling at a speed of 20 km/h that is 20 km east of your location. Will it reach you?
                                                                                                                                                                 
<Associated Press, 2008>

19. Velocity
Suppose there is a storm nearby traveling at a speed of 20 km/h that is 20 km east of your location. Will it reach you?
Knowing the speed is not enough; you must also know the direction it is traveling.
Velocity is the speed of an object and the direction it is moving.

20. How do speed & direction affect velocity?
Two escalators may move at the same speed even though one goes up and the other travels down.
Because they move in opposite directions their velocity is different despite having the same speed.
Velocity depends on both speed and direction.
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21. Motions of Earth’s Crust
Some motion is so slow that it is hard to see such as plate tectonics. Geologic evidence shows that the continents have moved over millions of years.
The plates of the lithosphere slide on the softer layers below manifesting themselves as earthquakes, volcanic eruptions and formation of mountains.
The plates along San Andreas Fault speed along at about 1 cm/yr!
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22. Section 2 - Acceleration
What You’ll Learn:
How acceleration, time & velocity are related
How positive & negative acceleration affect motion
How to calculate acceleration

23. Acceleration, Speed, & Velocity
Acceleration is the rate of change of velocity. When velocity changes, the object is accelerating.
Speed is the rate of change of position.
Remember velocity includes both speed & direction.

24. How are speeding up & slowing down described?
Speeding up & slowing down are both accelerating.
The first is positive and the second is negative.
Acceleration has direction, just like velocity.
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25. Does changing direction affect acceleration?
The speed of a horse moving around a carousel remains constant, but because it is changing direction it is accelerating.

26. Calculating Acceleration
Find the change in velocity by subtraction.
∆V= final V – initial V or Vf – Vi
Then, to find acceleration, divide ∆V by the length of time during the velocity change.
Acceleration (α)= ∆v or Vf – Vi /time (t)
where ∆ means change, V is velocity, α is acceleration, etc.

27. Calculating Acceleration
The SI unit for velocity is meters/sec (m/s).
To find acceleration, velocity is divided by time in seconds (s).
The unit for acceleration is m/s2.
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28. Amusement Park Acceleration
Roller coasters are exciting rides because their designers use the laws of physics.
The steep drops and loops of steel roller coasters give the rider large accelerations by using gravity and sharp turns.
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29. Section 3 – Motion & Forces
What You’ll Learn:
How force & motion are related
Newton’s first law of motion
What forces & motion are present during a car crash

30. What is force? Force is a push or a pull like kicking a soccer ball.
Sometimes it isn’t so obvious. Can you feel gravity holding you in place?
You exert force when you sit, stand, stretch, bend, push or pull.
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31. How does force change motion?
What happens to the motion of the ball when the racket hits it?
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32. How does force change motion?
What happens to the motion of the ball when the racket hits it?
The force of the racket makes the ball stop and then move in a different direction.
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33. What are balanced forces?
When 2 or more forces act on an object at the same time, the combined force is called net force. Forces that are equal in size & opposite in direction are called balanced forces.
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34. What is the result of unbalanced forces?
If both students push equally in opposite directions, the book does not move.
If the student on the right pushes harder as shown, movement will be to the left.
Net force is the sum of all forces acting on the object.

35. Inertia and Mass
Inertia is the tendency of an object to resist any change in its motion.
If it’s moving, it will keep moving until a force changes either its direction or speed.
A dirt bike will move in a straight line with a constant speed until a force acts on it. A force can turn the wheel to change direction or friction can slow the speed.
If it’s motionless, it still has inertia & will remain motionless until an unbalanced force causes it to move.
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36. Why can different objects have different inertia?
Inertia is related to the mass of the object.
Mass is the amount of matter in an object.
A bowling ball has greater inertia than a table tennis ball.
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37. What are Newton’s laws of motion?
British scientist, Sir Isaac Newton, stated rules that describe the effects of forces on the motion of objects.
They apply to all objects in motion from billiard balls to planets.
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38. What is Newton’s First Law of Motion?
An object moving at a constant velocity keeps moving at that velocity unless an unbalanced force acts on it.
An object at rest remains at rest unless a net force acts on it.
Newton’s first law of motion is sometimes called the law of inertia.
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39. What happens in a crash?
The law of inertia explains what happens in a car crash. Passengers who are not wearing a safety belt continue to move at the original speed of the car despite the car coming to slamming halt.
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40. How do safety belts help?
A person wearing a safety belt is attached to the car so they will slow down as the car slows down.
The safety belt prevents the passenger from slamming into the dashboard, windshield, or seat backs.
It also helps prevent people from being thrown from the car. Half the people who die in crashes would survive if they wore safety belts.

41. In a 30 m.p.h. collision an … <http://fonzation.com>
In a 30 m.p.h. collision an unbelted 160 lb. Person can strike another passenger, crash through a windshield and/or slam into the vehicle’s interior with a 4,800 lb. force.                                                                
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