1. Energy and Motion
Chapter 4

2. Energy and Motion
Have you seen a cheetah run?

3. Energy and Motion It can run 200 meters in 7 seconds.
It can accelerate from 0 to 29 meters in 3 seconds.
What do these numbers tell us about speed?
Chapter 4 will help us make sense of these numbers.
Laws of Motion
All motion involves energy
Different forms of energy
Learning how energy can change from one form to another

4. Energy Have you ever tried to use your phone but the battery was dead?
The phone won’t work because it had no more energy inside of it.
Energy is “the ability to do work.”
Without energy no work can be done.
A moving object has the energy of motion, called kinetic energy.
When a car is moving it can do work.
It can overcome road friction and air resistance and keep going forward.
The amount of kinetic energy a moving object has depends on the objects mass and speed.
The greater the mass or speed, the greater the kinetic energy.

5. Energy
Some objects are not moving but have the potential to move because of their position. These objects have stored energy.
This stored energy is called potential energy.
A book sitting on the floor has no potential energy and cannot work.
If you set a book on the edge of a table it has stored energy.
It can do work by falling to the floor.
The books potential energy changes to kinetic energy as it falls.
The higher the table the greater the potential energy.
Another example of potential energy is the spring of a mouse trap.
It does work as it snaps shut.

6. Forms of Energy
The energy you use to do work exists in six main forms.
All six forms can be stored.
All six forms can produce motion.
Six forms of Energy:
Chemical
Heat
Mechanical
Nuclear
Radiant
Electrical

7. Chemical Energy
Chemical Energy is stored in the bonds between atoms.
When substances react they can release some of the chemical energy in the substances and warm the surroundings.
Example: Burning coal produces heat.

8. Heat Energy
Heat energy is associated with the moving particles that make up matter.
The faster the particles move the more heat energy is present.
All matter has some heat energy.

9. Mechanical Energy
Mechanical energy is the energy in moving objects.
Objects, such as a moving bicycle, wind, and falling rock, have mechanical energy in kinetic form.
Sound is a form of mechanical energy.

10. Nuclear Energy
Nuclear energy is energy that is stored in the nucleus, or center of an atom.
It can be released in devices such as nuclear power plants and atomic weapons.

11. Radiant energy is associated with light.
Some energy that earth receives from the sun is in the form of light energy.

12. Electrical Energy
Electrical energy is energy that causes electrons to move.
Electrons are negatively charged particles in atoms.
Appliances such as refrigerators and vacuum cleaners use electrical energy.

13. Forms of Energy Energy can be changed from one form to another.
Example: Electrical Power Plant
Chemical energy is converted to heat energy when fuel is burned.
The heat energy is used to make steam.
The steam turns a turbine and produces mechanical energy inside a generator.
The generator converts mechanical energy into electrical energy by moving coils through a magnetic field.

14. The Law of Conservation of Energy
Energy can change form, but it does not disappear.
You can add energy to an object or take energy away, but the total amount of energy does not change.
Law of Conservation of Energy: Energy cannot be created or destroyed.
Example: Book falling from a table.
As a book falls, its potential energy decreases/the kinetic energy increases by the same amount.
The total amount of energy (potential plus kinetic) stays the same.
Just before the book hits the ground, its potential energy is approaching zero and all the energy becomes kinetic.
After the book hits the ground, the kinetic energy is changed into heat energy which causes a temperature change in the book and the ground.
The energy form changes but the total remains the same.

15. Motion and Speed
Chapter 4: Lesson 2

16. Motions and Speed Objects changing position in space. Examples:
Car carrying you from place to place.
Walking to the store.
Earth travels in space.
All change, including changes in position, take place over time.
To understand motion you must measure the passage of time.

17. Elapsed Time To answer this question you must calculate elapsed time.
Elapsed time is the amount of time that passes from one event to another.
To calculate elapsed time subtract the time of the earlier event from the time of the later event.
Example: A plane trip has just taken you from Miami to New York in the same time zone. Your flight began at 8:00 p.m. and ended at 11:00 p.m. How long did this trip take?

18. Speed Speed tells you how fast an object is moving.
Speed uses two units: Time and Distance.
Distance is the length of the path travelled by the object in motion.
Use the following formula to find the speed of an object.
Suppose the airplane mentioned earlier traveled 810 miles between the two cities. The elapsed time for the trip was 3 hours. Use the formula to find the speed of the airplane.

19. Speed The speed of the airplane is 270 miles per hour.
It is unlikely that the plane travelled at a constant speed of 270 miles per hour during the entire flight.
Speed varies during the trip (take off, landing, turbulence, etc.)
The speed calculated is actually the average speed.
Actual speed (instantaneous speed), could be more or less than the average speed at a given time.

20. Speed Speed does not have to be measured in mph.
Example: A race around a track is typically 400 meters. Suppose a runner completes the race in 50 seconds. What is the runner’s average speed?

21. The Laws of Motion
Chapter 4: Lesson 3

22. Isaac Newton
Sir Isaac Newton was a scientist who lived 350 years ago. He studied changes in the motion of objects. From his studies, he came up with three laws to explain motion.

23. The First Law of Motion
Newton’s first law of motion states that if no force acts on an object at rest, it will remain at rest. The law also says that if the object is moving, it will continue to moving at the same speed and in the same direction if no force acts on it.

24. The First Law of Motion
If you want to move a box that is on the floor you must either pick it up or push it.
The act of pushing or pulling is called force.
When an object changes its velocity or accelerates, a force causes the change in motion.
Acceleration refers to the rate of change of velocity.

25. The First Law of Motion
A car on a flat surface will roll to a stop if you take your foot off of the gas pedal.
The car slows down because of an invisible force at work.
The invisible force is friction.
Friction: a force that opposes motion and occurs when things slide or roll over each other.
The rougher the surface, the greater the friction.
In the example of the car there is friction between the road and the moving tires as well as the car and air resistance.

26. The First Law of Motion An tends to resist changes in motion.
This tendency to resist changes in motion is called inertia.
The inertia of an object depends in its mass.
The greater the mass of an object, the greater the force needed to cause a change in the objects motion.
Example: Think of pushing boulders.

27. The Second Law of Motion
Newton’s second law of motion says that the amount of force needed to produce a given change in the motion of an object depends on the mass of the object. The larger the mass, the more force is needed to give it a certain acceleration.

28. The Second Law of Motion
Think of driving a U-Haul truck to the moving location. After filling the U-Haul you drive to your new home. Now that the truck is full it will take longer to reach the same speed than it did when the truck was empty. What causes the difference?
The truck of furniture has more mass than the empty truck.
If you apply the same force (push the gas pedal the same amount) to the truck both times the truck with the furniture (more mass) will take longer to reach a given velocity.

29. The Second Law of Motion
Newton’s Second Law can be written as follows:
Force = mass x acceleration or F = ma
A small force acting on a large mass will cause very little change in motion.
A large force acting on a small mass will cause a larger change in motion.

30. The Third Law of Motion
Newton’s third law of motion says that if an object exerts a force on a second object, the second object will always exert a force on the first object. The force will be equal to the force exerted by the first object. But the force will be in the opposite direction. The law is sometimes stated: For every action, there is an equal and opposite reaction.

31. The Third Law of Motion
Example: Boy on a skateboard…

32. Gravity
Chapter 4: Lesson 4

33. Law of Universal Gravity
Gravity is a force of attraction between any two objects that have mass.
Gravity keeps you from flying off the face of the earth.
The gravitational force between two objects depends on the product of the masses of the two objects.
Example #1: The earth and the moon are two objects that have large masses. The gravitational force between them is large.
Example #2: Smaller objects such as people, trees, and buildings, have a much smaller gravitational force because they have a smaller mass. These forces are so small that they are difficult to observe.

34. The Law of Universal Gravity
Example: Astronaut…

35. The Law of Universal Gravity
The gravitational force of the sun, acting on the earth, keeps it in orbit.
The gravitational force prevents the earth from floating away into space.
Gravity also keeps the planets in space.
Each planet exerts a gravitational force on nearby objects.

36. Law of Universal Gravity
Law of Universal Gravity: gravitational force depends on the product of the masses of the two objects involved, and the gravitational force depends on the distance between the objects.

37. Gravity and Acceleration
Have you ever jumped from a short and a tall diving board?
From the higher board you fall faster, and you hit the water faster.
That is because the force of gravity causes an object to speed up as it falls.

38. Gravity and Acceleration
Gravity causes all objects to have the same acceleration as they fall.
Acceleration is the rate of change in velocity.
But, another force, air resistance, acts on falling objects.
Remember that air resistance is a form of friction
Friction is caused by molecules of air rubbing against a moving object.
Air resistance causes objects to fall at different speeds.
The amount of air resistance acting on a moving object depends on the shape of the object.
Example: different form/shapes of paper.