8th Grade Science Midterm Review
Put all answers on a separate sheet of paper.
v = Δd / Δt
a = Δv / Δt
ag = 10 [m/s2]
F=ma
D=m/V
V=lwh
V = π r2 h
π = 3.14
Fg = m ag
d = ½ a Δt2
1. Describe the size of a meter, second, and kilogram.
Meter=the floor to the door knob, a second= the time of one heart beat, a kilogram=a box of
dominos
2. What are metric units for distance, time, speed, acceleration, force?
distance= [m] time= [s]
speed=[m/s] acceleration=[m/s2]
force=N
3. What are the following pieces of lab equipment used for: the meter stick (distances), the stop
watch (time), the graduated cylinder (volume), the thermometer(temperature), the electric
balance(mass or weight), and the basic mass balance(mass).
4. List the steps of the scientific method.
Problem, Hypothesis, Experiment, Analysis, Conclusion, Report Data
5. Explain the parts of a good hypothesis.
must answer the problem question, must be testable, made before the experiment is done
6. What is done in the analysis section?
Organize data, make Graphs, Do calculations, answer questions
7. Explain the parts of a good conclusion.
Has to accept or reject hypothesis, must support the answer with data, decide if there is a new
question and if not, end the lab
8. What are independent and dependant variables?
Independent Variable= the part of the experiment you control or change
Dependent Variable=the part of the experiment you observe and measure
9. What is the difference between a control and a variable?
A control is the part of the experiment you do not test (it is the same for all trials), a variable is
what changes from trial to trial (the part you change)
10. What are the rules of density?
If an object is more dense than the surrounding fluid, then it will sink
If an object is less dense than the surrounding fluid, then it will rise
If an object has the same density as the surrounding fluid, then it will suspend
If two objects are both more dense than the surrounding fluid, the denser one sinks
faster
11. Rank the states of water from lowest density to highest density.
Gas-Lowest Density, Solid (ice)-Middle Density, Liquid(water)-most dense
12. How are mass and weight different?
Mass does not change from place to place in the universe because it is a measure of an objects
inertia, weight does change because it is the force of gravity and gravity varies from place to
place.
13. How does a basic balance work? How does a triple beam balance work?
The Basic Scale
1. Empty both of the pans
2. Put the object with unknown mass on one of the pans
3. Put known masses on the other pan until it balances out
4. Add up the known masses (this will be the mass of the unknown object)
The Triple Beam Balance
1. Clear off the pan and move the weights back to zero
2. Make sure the scale is balanced (turn little knob under pan to get lines to line up at zero)
3. Put the unknown mass on the pan
4. Move the large weight to the last spot that does not tip the scale
5. Move the medium weight to the last spot that does not tip the scale
6. Move the small weight until it balances out
7. Add up the three values (this will be the mass of the unknown object)
14. How does an electric balance work? How can you find the mass of an object that rolls around?
Electronic Balance
1.
2.
3.
4.
5.
Plug it in and turn it on
Select the unit that you want the balance to measure
Press the “zero” button
Put the object with the unknown mass on the pan.
Read the displayed value
to find the mass of an object that rolls around, place a pan on the balance then zero the
balance and put your object in the pan to find its mass.
15. Find the density of a 20 g rock that has a volume of 4 cm3.
𝑚
20𝑔
D=
= D= = 5 g/ cm3
𝑉
4cm3
16. How can you use a graduated cylinder to find the volume of an object?
1. Put some water in a graduated cylinder
2. Measure the volume of the water (ex: 65 mL)
3. Put your object completely under water (may use a pencil to push floating objects just below
the water line)
4. Read the new value of volume (ex: 75 mL)
5. Subtract the new volume from the original volume (ex: 75 mL- 65 mL)
6. The subtraction gives the volume of the object (ex: 10 mL)
17. How can you find the volume of a rectangular cube, and a cylinder?
For a box use Volume= length x width x height
For a cylinder use Volume= πr2h
18. How are speed and velocity different?
Speed is a change in position over a change in time and velocity is simply a change in position
over a change in time with a direction
19. Find the average speed when someone drives 40 miles, then 20 miles, then 10 miles, then 5
miles in a total time of 3 hours.
40+20+10+5=75/3=25 mph
20. What does the slope mean on a position graph?
A slope on a position graph is speed.
21. What does at rest look like on a position graph?
A flat line
22. What does constant speed look like on a position graph?
A diagonal line (pointed up= moving forward, pointed down=moving backwards)
23. What does acceleration look like on a position graph?
A curved line
24. What does an object do when there is net force acting on it?
When the net force is not zero, the object accelerates (speed up, slow down, change
direction)
25. What force is needed to push a 4 kg object with an acceleration of 5 m/s2.
F=ma F=4 x 5 F=20N
26. A mouse and an elephant are dropped out of a window (don’t worry there is a bouncy house
bellow), which animal gets to the bouncy house first?
they will reach the bouncy house at the same time because both fall at the same speed being
pulled by gravity.
27. What is gravity, how much is it, and which way does it point?
Gravity is an acceleration (the force of attraction between an object and the planet that it
is on). It is 10 m/s2 on Earth and points down toward the center of the Earth (because
the Earth has more mass than you)
28. What two things can an object do when the forces acting on it balance out?
An object at rest will remain at rest and an object in motion will remain in motion at a constant
speed and direction.
29. What are the three things an object can do when there is a net force acting on it?
speed up, slow down, change direction
30. Describe Physical changes, and provide an example.
a change in a substance that does not change what the substance is Ex: cutting a loaf of bread,
dying hair
31. Describe Chemical changes and provide an example.
a change in a substance that does change what the substance is (irreversible) Ex: Baking
cookies, burning gasoline
32. Describe two different ways to tell which of two objects has a greater density.
Place them in water and see which one sinks to the bottom the fastest or put a scale under
water and whichever side tips down has the greater density. Third way- put item on a balance to
find the mass then use a graduated cylinder to find the volume then use both numbers and
solved the density equation.
33. What is a molecule?
the smallest part of a substance that is still that substance
34. Describe a solid, liquid, gas, and plasma.
Solid- a substance with a constant shape and constant volume
Liquid- a substance with a variable shape and constant volume
Gas- a substance with a variable shape and variable volume
Plasma- a substance that has only charged particles
35. Draw a picture of a box at rest on a hill, and draw arrows for the forces of gravity, normal force,
and friction.
FN
Ff
Fg
36. Find the speed of a cheetah that can run 24 meters in 2 seconds.
∆𝑑
v=
∆𝑡
24
v=
2
V= 12m/s
37. Find the acceleration of a car that speeds up from 10 to 30 m/s in a time of 4 seconds.
a=
∆𝑣
∆𝑡
a=
20
4
a=5m/s2
38. Find how far a ball dropped from rest falls after 2 seconds.
d=½ at2
d=1/2 (10)(22) d=1/2 (10)(4) d=1/2 (40)
39. How are meteoroid, meteor, and meteorite different?
d=20 meters
Meteoroid- a rock located in space
Meteor- a space rock that burns up before hitting the ground (a.k.a shooting stars)
Meteorite- a rock from space that makes it to the ground before burning up
40. How does an asteroid differ from a comet?
Asteroid- a very large space rock
Comet- a mass of ice, dust, and gas traveling through space (the tail is the gas of
evaporated ice)
41. Earth is special because it has lots of water. What percentage of the surface is covered in water
and land?
71% water
29% land
42. What are two most common gasses in our atmosphere?
78% Nitrogen, 21% Oxygen
43. List the three main services provided by the Earth’s atmosphere.
smoothes out temperatures, moves resources, provides a protective shield from harmful space
radiation
44. Why does the temperature on the moon get a lot more extreme than the temperatures on
Earth, even though both places are nearly the same distance from the sun?
The moon does not have an atmosphere
45. How long does it take the earth to rotate once, and what is this called?
24 hours- it’s called a day
46. How long does it take the earth to revolve once around the sun, and what is this called?
365.25 days- it’s called a year
47. How long does it take the moon to revolve once around the Earth, and what is this called?
29 days- it’s called a month
48. Explain why the Earth has seasons?
Earth’s tilt causes earth to have 4 seasons (tilt toward sun= summer, tilt away=winter)
49. What causes tides on Earth? When causes high tide to occur?
The gravity of the moon causes tides. high tide is when the moon is directly above the
water
50. How is it possible to see the moon, even though it is not a star?
The moon can be seen at night because it reflects sunlight
51. What happens in a lunar eclipse?
the earth’s shadow falls on the moon causing it to look dark (Sun- Earth- Moon)
52. What happens in a solar eclipse?
the moon casts a shadow on the earth and blocks out the sunlight (Sun-Moon-Earth)
53. List the phases of the moon.
54. What is the sun, what is it made out of?
a star- made up of a large ball of burning gases (hydrogen and helium)
55. What is a light year? What does it mean to say something is 10 light years away?
light year-the distance light travels in one year. To say it is ten light years away means
that it takes light ten years to travel from a location and reach us.
56. What is a solar system?
a star and the planets that revolve around it
57. What is a constellation?
a grouping of stars
58. What is a galaxy?
a collection of millions of constellations
59. What is the Universe?
a collection of everything
60. What is the reason for the different values of gravity on each planet in our solar system?
The planets in the solar system each have different masses, some larger than others, so they will
have more gravity