1. Forces
Newton’s First Law

2. What is a Force? A push or pull on an object.
Some forces are seen, for example a box being pushed across the table.
Some forces are not seen, for example the floor pushing up on your feet.

4. Balanced Forces
A balanced force is a force on an object that is equal in size and opposite in direction.
Tug of war is a good example.
Each person is pulling on the other with an equal and balanced force.

7. Unbalanced Forces Sometimes forces are not equal or opposite.
Example: Pushing a car.
An unbalanced force is a net force.
A net force acting on an object will change the velocity and/or direction.

9. Why do objects stand still if no force is applied?
Inertia!
The tendency of objects to resist a change in motion.
If it is moving – it will keep moving.
If it is still – it will not move.
UNLESS….. A net force acts on it!

10. Inertia
Examples:
A book on your desk will sit there and not move, unless you apply a force to the book to move it. If your arm pushed the book, that would be a force.
If you drive in a car and hit a wall without the force of a seat belt to stop you, your body will continue to move even though the car has stopped. This is why people go through the windshield.

13. Which object has more inertia?
Heavier objects are harder to stop moving and start moving.
The larger the mass, the greater the inertia.
Example: A semi truck is harder to stop than a toy truck.

14. Newton’s First Law of Motion (Law of Inertia)
“An object moving at a constant velocity will keep moving at that velocity unless a net force acts on it. If an object is at rest it will stay at rest unless a net force acts on it.”
An object in motion will stay in motion (rest at rest)
Hmmm- Isn’t that Inertia?

16. Why don’t object stay moving forever????
If the Law of Inertia is true, than any moving object should move forever!
In outer space this is true because there is no friction.

17. What is Friction?
The force that pushes in the opposite direction of motion between two surfaces that are touching each other.
For Example: A car will eventually slow down because of the friction between the car tires and the road.

19. Newton’s Second Law
Notes 4.1

20. Newton’s Second Law of Motion
This Law is best explained as an equation.
Force = mass x acceleration
The net force acting on an object causes that object to accelerate in the direction of the force.

22. Newton’s Second Law of Motion Example:
How much force is needed to accelerate a 70 kg rider and her 200 kg motorcycle at 4 m/s2?
F = m x a
F = 270kg x 4 m/s2
F = 1080 kgm / s2 or N

23. What is a Newton? F = m x a F = kg x m/s2 F = kg m s2
1 kg m = 1 Newton

24. Gravity
Notes 3.5

26. What is Gravity? The force in the universe between all objects.
Every object in the universe exerts a force on other objects.

27. Gravitational Force
The amount of force that gravity exerts is called gravitational force.
How much gravitational force there is depends on the mass and distance between objects

28. Gravitational Forces Example
Earth is larger than the moon, therefore the moon is stuck in the gravitational pull of the earth.

29. Gravity and Weight
The measure of the force of gravity on an object is weight.
Weight is different from mass!!!

30. Mass vs. Weight Definition Measuring Tool Unit Location Mass
The amount of matter in an object
Balance
g, kg
Not changed by location
Weight
Amount of gravitational force acting on an object
Scale
Newton
(N)
Changed by location

31. Mass vs. Weight Mass is not a force. It is a quantity.
Weight is the force of gravity on an object.
A mass of 1 kg weighs 9.8 N.

32. How do I calculate weight?
Because any force can be calculated using the equation F = m x a, weight of an object (a force) can be calculated using a similar equation W = m x a.
Because weight is the force of gravity on an object the rate of acceleration is the pull of gravity. (remember? 9.8 m/s2)

33. Weight Example W = m x g (g = gravity)
If a person has a mass of 50 kg what is their weight?
W = m x g
W = 50 kg x 9.8 m/s2
W = 490 N

34. Acceleration Caused by the Force of Gravity
Gravity is a force that pulls objects towards the center of an object. (Earth)
Near the Earth’s surface, gravity causes all falling objects to accelerate at 9.8 m/s2.
Acceleration due to gravity is the same for all objects.

35. The bowling ball and the feather…
If acceleration due to gravity is the same for all objects, regardless of mass, then all objects should fall at the same rate.
Does a leaf fall as fast as an acorn?

36. Air Resistance
Two objects will only fall at the same rate if no other force is present.
For example: in outer space
On Earth we have Air Resistance.
The force that air exerts on a moving object.
This force acts in the opposite direction of the objects motion.

37. Air Resistance Example
If you drop two pieces of paper, one whole and the other crumpled up into a ball- which would hit the ground first?
The crumpled ball because there is less air resistance.
Air resistance pushes up as gravity pulls down.

38. Air Resistance
The amount of air resistance on an object depends on the speed, size, shape and density of the object.

39. Action and Reaction
Newton’s Third Law

40. Newton’s Third Law
For every action, there is an equal and opposite reaction.
For example: If you jump out of a boat the boat exerts a force on your feet pushing your forward, although your feet exert an equal and opposite force on the boat sending it backwards.

42. Unbalanced action - reaction pairs
Sometimes action and reaction forces are not balanced.
For example, if a toy truck rolls towards you, you can stop it with your hand. The action of the truck is not equal to the force of your hand.

44. Momentum
While you can stop a toy truck with your hand, you would not be able to do the same for a pickup truck.
It takes more force to stop a pickup truck than a toy truck. This is because of Momentum.

45. Momentum = mass x velocity
Momentum is the strength of motion due to the mass and velocity of the object.
The Momentum of an object can be calculated.
Momentum = mass x velocity
p = m x v
kg x m/s

46. Momentum Practice Problem
A 4 kg bowling ball rolling at 6 m/s hits a bowling pin. What is the momentum of the bowling ball?
p = m x v
p = 4kg x 6 m/s
p = 24 kgm/s

47. Conservation of Momentum
The momentum of an object does not change unless the mass or velocity of the object changes.
However- momentum can be transferred from one object to another.
The total amount of momentum does not change unless an outside force acts on the object(s).

48. The Energy of Motion
Notes 5.1

49. What is Energy Is the ability to cause change
Many different forms of energy
Chemical
Electrical
Thermal
Nuclear

50. Kinetic Energy The energy in the form of motion
The amount of Kinetic Energy depends on the mass and velocity of the moving object.
More mass = more KE
More Velocity = more KE

51. Potential Energy The stored energy of position.
A flower pot on a window ledge has the potential to fall.
Potential energy depends on position.
A flower pot on the fifth floor has the ability to cause greater change than a flower pot on the first floor.

52. Relationship between PE and KE
Mechanical Energy is the total amount of Kinetic and Potential Energy in a system.

54. Conservation of Energy
Energy can not be created or destroyed, it can only change form.

55. Conservation of Energy
Pendulums

59. How do we transfer energy?
Work is the ability to transfer energy through motion.
The amount of work done can be calculated.
W = F x d

60. Work
Definition: The transfer of energy through motion. A force is exerted over a distance.
Equation: W = F x d

61. Practice Problem:
A dancer lifts a 400N ballerina overhead a distance of 1.4 m. How much work has he done?
W = F x d
W = 400N x 1.4m
W = 560 N  m
W = 560 J

62. Practice Problem:
A game show contestant won a prize by pushing a bowling ball 20m using his nose. The amount of work done was 1470J. How much force did the person exert on the ball?
F = W / d
F = 1470J / 20m
F = 73.5 N

63. Machines
Notes 7.1

64. What is a Machine? A machine is any device that makes work easier.
Some machines are powered by engines or motors, others are simple and only require one movement.

65. Machines: Making Work Easier by….
Lifting our cars (jacks)
Helping us climb (stairs)
Moving us (wheels and axles)

66. Machines
An ideal machine would have the work output equal to the input.
Machines help to overcome obstacles like gravity and friction.

67. What are Machines?
A device that makes work easier by changing the force.
They change the size of the force needed, the direction of the force or the distance over which a force acts.

68. Advantages of Machines
Can increase the amount of force on an object.
Lug nut
Can increase the distance that the force must work within
Pulley
Can change the direction of the force
Oar

69. Simple Machines There are six types of simple machines Levers Pulleys
Wheel and Axle
Inclined Plane
Screw
Wedge

70. Compound Machine A combination of two or more simple machines
A bicycle

71. Levers
Levers: A rigid bar that moves around a fixed point called a fulcrum.
When you put force into a lever it will produce a different amount of output force.

72. Levers
First Class Lever: The fulcrum is located between the input force and the output force.

73. Levers
Second Class: The output force is located between the input force and fulcrum.

74. Levers
Third Class: The input force is located between the fulcrum and the output force.

75. Simple Machines - Pulley
Pulleys are simple machines made from a rope that fits into the groove of a wheel.
Types of pulleys
Fixed
Movable
Pulley System

76. Simple Machines: Wheel and Axle
A ‘Wheel and Axle’ is a simple machine that consists of two disks (or cylinders), each one with a different radius.

77. Simple Machines: Inclined Plane
An Inclined Plane is a slanted surface that can move an object at a different elevation.

78. Simple Machines: Screw
A Screw is an inclined plane wrapped around a cylinder.
Screws with threads that are closer together have a greater ideal mechanical advantage.

79. Simple Machines: Wedge
A Wedge is a V-shaped object whose sides are two inclined planes sloped towards each other.

80. Power Definition: Power is the rate of doing work. Equation:
To increase power you whether increase the work done in a given time, or do the amount of work in less time.
Equation:
Power = work / time
Remember!!! Work = Force x distance

81. Power Practice Problems:
A figure skater lifts his partner, who weighs 450N, 1.0m in 3.0s. How much power is required?
Power = work / time
Power = (Force x Distance) / time
Power = (450N x 1.0 m) / 3.0 s
Power = 450 J / 3 sec
Power = 150 J/s or…… 150 W (Watts)

82. Watts Watt is the SI unit for power.
It represents the amount of Joules per second
For example, a 40 Watt light bulb requires 40J of energy for every second that it is lit.