1. Forces, Waves, and Electricity
Georgia High School Graduation Test: Science Review

2. Speed and Velocity Speed = distance divided by time s = d/t
Units of speed = m/s
Velocity = speed in a given direction
Example:
55 mph = speed
55 mph north = velocity

3. Distance versus Time Graph
AKA position versus time graph
Straight line represents constant (uniform) speed

4. Acceleration Acceleration = rate at which velocity changes
Involves a change in speed OR direction
a = (vf – vi )/ t
Units of acceleration = m/s2
Example: 0 to 60 mph in 5 seconds
For acceleration to occur a net (unbalanced) force must be applied

5. Distance versus Time Graph Revisited
Non-linear graph represents acceleration
Parabola = constant acceleration

6. Sample Question #1
Use the equations for velocity and acceleration to solve the following examples:
A ball rolls in a straight line very slowly across the floor traveling 1.0 meter in 2.0 seconds. Calculate the velocity of the ball.
Answer: v = 0.50 m/s
If the ball from the above question rolls to a stop in 2.0 seconds, calculate the acceleration (deceleration) of the ball.
Answer: a = m/s2

7. Newton’s 1st Law of Motion
An object at rest will remain at rest and an object in constant motion will remain in constant motion unless acted on by an unbalanced force.
Reason for seatbelts

8. Newton’s 2nd Law of Motion
A force is a push or a pull
Force = mass x acceleration
F = ma

9. Net Force More than one force can act on an object at once.
For example, if one person pushed the book with a force of 20 Newtons toward the left, and the other person pushed the book with a force of 18 Newtons toward the right, then that the net force would be 2 Newtons in size and directed toward the left. This produces an ‘unbalanced’ force which produces motion.
                                                            

10. Frictional Force
Friction is the force that always opposes (acts in the opposite direction) motion.
Examples are:
- rubbing your hands together to produce heat
- car tires against the road
- air resistance (drag)

11. Newton’s 3rd Law of Motion
For every action, there is an equal but opposite reaction
Examples:
Punch a wall, it punches back
Rocket propulsion

12. Gravity Gravity = attractive force between two objects that have mass
Makes falling objects accelerate (g = 9.8 m/s2)
Depends on mass and distance

13. Sample Question #2 What causes an object to accelerate as it falls?
Answer: The force of gravity causes an object to accelerate at a rate of 9.8 m/s2 toward Earth.

14. Mass versus Weight MASS measure of the amount of matter in an object
measured in kilograms
does not depend on location
an object’s mass on Earth is the same as its mass on the Moon
WEIGHT
measure of the force of gravity on an object
measured in Newtons
does depend on location
an object’s weight on Earth is more than its weight on the Moon

15. Sample Question #3 Explain the difference between mass and weight.
Answer: Mass is the quantity of matter of an object while weight is the measure of the force of gravity on that object. Mass is conserved while weight may change depending on location.

16. where force and distance are in same direction
Energy and Work
Energy = The ability to do work
Work = transfer of energy by applying a force to move an object
W = Fd
where force and distance are in same direction
Both work and energy are measured in Joules

17. Examples of Work and No Work
Hammer applies a force to move the nail in the same direction = WORK
Waiter applies a force upward while the tray moves forward = NO WORK

18. Sample Question #4
Use the formula for work to solve the following example:
A woman picks up her 10 Newton child lifting him 1 meter. She then carries him 5 meters across the room. How much work is done on the child?
Answer: 10 Joules
the 5 meters is not added to the 1 meter because the distance moved (5 meters) is perpendicular to the force applied

19. How do you calculate the MA of a machine?
The MA is the mechanical advantage of a simple machine. It is a measure of how much the machine amplifies (multiplies) the force.
A machine is a device that makes work easier.
How does it make work easier?
1. change magnitude of force
2. change the direction of the force

20. Inclined plane
length
height
IMA = length / height

21. Mechanical Advantage Actual Mechanical Advanatge (AMA)
the ratio of resistance force (Fr) to effort force (Fe)
Ideal Mechanical Advanatge (IMA)
the ratio of effort displacement (de) to resistance displacement (dr)
AMA = Fr Fe
IMA = de dr

22. WHAT ARE WAVES?
Rhythmic disturbances that carry energy through matter or space.
May or may not require a medium.
Mediums may be liquid, gas or solid
2 types of waves
Mechanical – sound, water (require medium)
Electromagnetic – radiation, light, UV (do NOT
require a medium)

23. Light Light is a form of electromagnetic radiation (EM)
EM spectrum shows the forms of radiation in order of increasing frequency (and energy) and decreasing wavelength

24. Cell Phones
Long wavelength & low frequency
Lowest photon energy TV
Radio Telescopes
Radios

25. MICROWAVES Shorter wavelength & higher frequency than radio
Used in communication
Used in cooking

26. Color of Light
We see different colors depending on the frequency of light emitted or reflected
This is the reason blue flames are hotter than yellow. Blue has a higher frequency so it has more energy.

27. Higher frequency than visible light
Has greater penetrating power
Used to kill bacteria & viruses in hospitals
Sunlight

28. Has the ability to travel through some matter
View broken bones
Used in airport scanners

29. Smallest wavelength & highest frequency
Most penetrating power
Used to kill cancerous cells

30. Sample Question #5
How are the frequency and wavelength related to the energy carried by waves?
Answer: Higher frequency waves have more energy while longer wavelength waves have less energy. Frequency and energy are directly related while wavelength and energy are inversely related. Radio waves (long wavelength) have less energy than gamma waves (high frequency).

31. Sample Question #6 How are frequency and wavelength related?
Answer: Frequency and wavelength are inversely related. High frequency waves have short wavelengths.

32. Electromagnetic Wave (EM) versus Mechanical Wave
EM WAVE
does not require matter to transfer energy
CAN travel through a vacuum
example: light
MECHANICAL WAVE
does require matter to transfer energy
CANNOT travel through a vacuum
example: sound

33. Sample Question #7 Compare electromagnetic and mechanical waves.
Answer: Electromagnetic waves (light) do not require matter to transfer energy while mechanical waves (sound) require matter to transfer energy. In other words, EM waves will travel in a vacuum while mechanical waves will not.

34. Reflection of Waves When waves strikes a boundary, it reflects.
The angle at which the wave approaches a flat reflecting surface is equal to the angle at which the wave leaves the surface (like a bounce pass of a basketball).
Reflection of light results in image formation.
Reflection of sound results in an echo

35. Refraction of Light
Light waves travel faster in air than in water and slower in glass than water.
More dense = slower light
When light enters a different medium, speed changes and it bends.
Bending of light due to change in speed = REFRACTION

36. Question?
What is happening in the following?
refraction

37. Wave Interference
the phenomenon which occurs when two waves meet while traveling along the same medium
constructive = waves add to produce a larger wave
destructive = waves cancel to produce a smaller wave
CONSTRUCTIVE
DESTRUCTIVE

38. Diffraction
Diffraction refers to the "bending of waves around an edge" of an object.
Diffraction depends on the size of the object relative to the wavelength of the wave

39. How does sound travel? Speed of Sound depends on 2 things
Temperature of medium
Medium through which it travels
The warmer the temperature of matter, the faster sound will travel.
The faster –moving the molecules in warm air bump into each other more often and transmit pulses faster.
At 20°C, sound travels about 340 m/s.

40. The Doppler Effect
observed whenever the source of waves is moving with respect to an observer
an apparent change in frequency occurs
toward = higher frequency; shorter wavelength
away = lower frequency; longer wavelength

41. Electricity Electrons carry a negative charge.
Lost electrons = positive charge
Gained electrons = negative charge
REMEMBER:
Like charges repel
Opposites attract

42. In conduction, electrons flow through one object into another by direct contact
Silver, copper, aluminum, and magnesium are examples of good conductors.
These materials allow electrons to flow freely.

43. Induction involves electrons being rearranged
Induction involves electrons being rearranged. No contact need occur between two objects for induction to take place. A neutral object only needs to approach a charged object.
For example, a negatively charged rubber rod picks up tiny slips of paper by induction. The electrons on the parts of the paper nearest the rod are pushed away leaving positive charges. Because the positive charges are closer to the negatively charged rod, the slips of paper are attracted to the rod.

44. Electrical Circuits Current flows in a closed circuit Ohm’s Law
SERIES
Current flows in a closed circuit
Ohm’s Law
V = IR
Two types of circuits:
Series (single path)
Parallel (poly paths)
PARALLEL

45. Electricity and Magnetism are related
Electricity has a + and – charge while magnetism has a north and south pole
Like charges repel, opposite charges attract; Like poles repel, opposite pole attract.
Charges have lines of force around them; magnets have lines of force around them.

46. Electromagnet
One can make an electromagnet with a nail, battery, and wire
When current flows through the coiled wire, the nail becomes magnetized.

47. Electromagnets: - transform electrical energy into mechanical energy
- Placing a metal core inside a coil of wire carrying an electric current produces electromagnets.
The current produces a magnetic field.
Increase Electromagnets by:
Increase the current
Increase the number of coils
Put in an iron core