1. 8th Grade Physical Science
Mass, Force and Motion
8th Grade Physical Science

2. S8P3. Students will investigate the relationship between force, mass, and the motion of objects.
Demonstrate the effect of balanced and unbalanced forces on an object in terms of gravity, inertia, and friction.

3. What is a force?

4. Calculating Net Forces A net force is the total amount of all forces acting on an object.

5. Add forces moving in the same direction
Add forces moving in the same direction. Subtract forces moving in opposite directions.

6. BALANCED FORCES vs. UNBALANCED FORCES
Balanced forces are always equal to ZERO and DO NOT cause motion.
Unbalanced forces ALWAYS cause motion and NEVER equal to zero.

7. FRICTION is a force that works in the opposite direction to motion.

8. Static Friction vs. Kinetic Friction
Static friction is found where there is NO motion.
Kinetic friction is found where MOTION occurs.

9. Newton’s 1st Law of Motion

10. Newton’s 1st Law of Motion or The Law of Inertia states…
Newton’s 1st Law of Motion or The Law of Inertia states….. An object at rest tends to stay at rest and an object in motion tends to stay in motion unless an unbalanced force acts upon it.

11. An object in motion will stay in motion forever unless an unbalanced force acts on it. Friction is just such an unbalanced force.   
Inertia is the tendency of all objects to resist any change in their motion or non-motion.
All objects with mass have inertia. Therefore, mass can be thought of as a measure of inertia.
The greater the mass, the greater the inertia.

12. 2nd Law – The Law of Acceleration

13. Newton’s 2nd Law of Motion

14. Newton’s second law describes the motion of an object when an unbalanced force acts on it.
Acceleration decreases as mass increases. Acceleration increases as force increases.
The acceleration of an object will be in the direction of the unbalanced (larger) force.

15. Newton’s 3nd Law of Motion

16. According to Newton’s 3rd Law of Motion, Forces Always Come In Pairs (or Twos)

17. The way that force pairs interact affects the motion of objects.
Force pairs do not act on the same object. If they did, the net force would be zero and no motion would occur.
Ex: A space shuttle pushes gas downward,
the shuttle is launched upward with equal
and opposite force.
Another force involved with action/reaction
is the normal force. The normal force is a
support force exerted upon an object that
is in contact with another stable object.
This is the force that supports the weight
of an object on a surface.

18. SI (International System) Units of Measurement We measure forces in NEWTONS. We measure weight in NEWTONS. Weight is measurement of the FORCE of GRAVITY. Gravity is a major force in the universe!

19. S8P5. Students will recognize the characteristics of gravity, electricity, and magnetism as major kinds of forces acting in nature.
a. Recognize that every object exerts gravitational force on every other object and that the force exerted depends on how much mass the objects have and how far apart they are.

20. Gravitational Force

21. The Force of Gravity and Mass

22. The Force of Gravity and Distance

23. S8P3. Students will investigate the relationship between force, mass, and the motion of objects.
a. Determine the relationship between velocity and acceleration.

24. Speed and Velocity
Both use the same equation:
Speed or Velocity = distance
time
Velocity has a direction…..Speed does not go in a particular direction.

25. Velocity and Acceleration

26. SI (International System) Units of Measurement We measure speed in m/s
SI (International System) Units of Measurement We measure speed in m/s. We measure velocity in m/s. We measure acceleration in m/s2. (Or…meters per second per second.)

27. S8P3. Students will investigate the relationship between force, mass, and the motion of objects.
c. Demonstrate the effect of simple machines (lever, inclined plane, pulley, wedge, screw, and wheel and axle) on work.

28. What Is Work? Work is the transfer of energy to an object.
In science, work is done when a force causes an object to move in the direction of the force.

29. Do forces always cause work?

30. How to Calculate Work
We use the equation W = F x D “Work equals Force times Distance”

31. SI (International System) Units of Measurement We measure work in J
SI (International System) Units of Measurement We measure work in J. J stands for Joule A Joule is a Newton times a meter. Joule = N x m

32. What is Power?
Power is the rate at which energy is transferred to an object.

33. How to Calculate Power P = W Power = Work t time
To calculate power (P), you divide the amount of work done (W) by the time (t) it takes to do that work, as shown in the following equation:
      
How to Calculate Power
P = W Power = Work
t time
In order to calculate Power, you divide the amount of work done (W) by the time (t) it takes to do that work.

34. SI (International System) Units of Measurement We measure power in W
SI (International System) Units of Measurement We measure power in W. W stands for Watt A Watt is one Joule per second. Watt = J/s

35. What is a Machine?
A machine is a device that makes work easier by changing the size or direction of the force.

36. Work Input and Work Output
When you use a machine, you do the work on the machine and the machine does the work on something else.
The work that you do on the machine is called the “work input”.
The work done by the machine is called the “work output”
The “work output” can never be more than the “work input”

37. Machines Can Change The Input Force

38. Machines Change the Size or Distance of an Input Force

39. Mechanical Advantage
Some machines increase force more than other machines can.
The amount of times that a machine multiplies the force is called
mechanical advantage.

40. Mechanical Efficiency
Mechanical efficiency is the comparison of a machine’s work output with the work input.
We measure it with the following equation:

41. Simple Machines
There are six basic simple machines that help make our lives much easier.

42. Inclined Plane
An inclined plane is a simple machine with a straight slanted surface. A ramp is an inclined plane.

43. Lever
A lever is a simple machine that has a bar that pivots about a fixed point called a fulcrum.
There are 3 types of levers:
1st Class nd Class rd Class

44. Pulley
A pulley is a simple machine that has a grooved wheel that holds a rope or cable.

45. Wheel and Axle
A wheel and axle is a simple machine that consists of two circular objects of different sizes.

46. Screw
The simple machine called a screw is an inclined plane wrapped in a spiral around a cylinder.

47. Wedge
The simple machine called a wedge is a pair of inclined planes that move.

48. Compound Machines
Compound machines are machines that are made up of two or more simple machines.