8th Grade Science Midterm Review
Put all answers on a separate sheet of paper.
v = Δd / Δt
a = Δv / Δt
ag= 9.81 [m/s2]
F=ma
Fg = m ag
d = ½ a Δt2
V=LWH
V = π r2 h
V = (4/3) π r3
D=m/V
Dwater = 1 [g/mL]
1. Describe the size of a meter, second, and kilogram.A meter is about the height of a door handle from the floor.
A second is about the time for one heart beat. A kilogram is about the mass of a text book.
2. What are metric units for distance, time, speed, acceleration, and force? A unit describes how an idea is
measured. Distance is measured in [m]. Time is measured in [s]. Speed is measured in [m/s]. Acceleration is
measured in [m/s2]. Force is measured in [N].
3. What are the following pieces of lab equipment used for: the meter stick, the stop watch, the graduated
cylinder, the thermometer, and the electric balance.A meter stick is used to measure distance. A stop watch is
used to measure time. A graduated cylinder is used to measure volume. A thermometer is used to measure
temperature. The electronic balance is used to measure mass or weight.
4. List the steps of the scientific method.1) State the problem: form a question for what you want to figure out. 2)
Background: learn about the topic you are asking a question about. 3) Hypothesis: answer the question such
that it is testable, and directly related to the content in the question. 4) Experiment: test the hypothesis. 5)
Analysis: organize the data, perform calculation, make graphs…, 6) Conclusion: accept or reject your hypothesis,
prove your position with data from the lab, and decided if you have a new question to pursue.
5. How many variables should you test at one time?One. Any more than one makes it unclear as to what caused
the change in an experiment.
6. Explain the parts of a good hypothesis.A good hypothesis clearly answers the question proposed in the problem
section of the lab. It is also testable. For example is the question is, “Does texting negatively influence the time
it takes to compete a Mario Kart course.” Then a good hypothesis would be “Sending a text message will
increase the time it takes to complete a Mario Kart race.” Notice how the hypothesis uses the same vocabulary
as the question, and does so in a way that makes the question testable. Now an experiment can be done in
which the results will either prove or reject the hypothesis.
7. What is done in the analysis section?Data collected in the experiment needs to be organized and worked with.
You may end up graphing, making a chart, performing calculations etc.
8. Explain the parts of a good conclusion.A good conclusion accepts or rejects the hypothesis. For example, “I
accept the hypothesis that texting increases the time necessary to complete a Mario Kart race.” Then you must
prove it. “The data shows that when not texting the average time to complete the Luigi Circuit was 2 minutes
and 12 seconds. However when sending 3 texts while driving the race the average time to complete the Luigi
Circuit was 3 minutes and 23 seconds.” Then you need to decide if there are any more questions. “I wonder if
the driver in the Mario Kart race just drives and person next to them does the texting while speaking out loud
will cause the same results.”
9. What are independent and dependant variables?An independent variable is something that you control in a lab.
A dependant variable is something you measure in a lab. For example you would control angle of a hill for an
independent variable, and then you would measure the speed of a ball at the bottom of the hill as a dependant
variable.
10. What is the difference between a control and a variable?A control is the one element that you do not test in a
lab. For example if you wanted to test which detergent gets grass stains out of a white shirt with the least
amount of washes, you may want to have one shirt that is washed in only water as the control. A variable is
anything that changes in an experiment. In the case of the grass stain experiment the different types of
detergent tested would be the variable.
11. How are mass and weight different?Mass is the amount of matter in an object and is measured in [kg]. Weight
is the force of gravity acting on an object and is measured in [N].
12. A cube is being measured with a ruler. The left edge is at 15 cm, and the right edge is at 40 cm. What is the
width of the cube?The width of the cube is 25 [cm]. This is the difference between 40 and 15 [cm].
13. 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.Average speed is equal to total distance divided by time. For 40 miles the average speed is 40/3 or
13.3 MPH, for 20 miles its 20/3 or 6.67 MPH, and for 5 hours its 5/3 or 1.67 MPH.
14. What does the slope mean on a position graph, and on a speed graph?On position graphs slope represents
velocity. Note the velocity is positive if the slope is positive (diagonal up and right). The velocity is negative if
the slope is negative (diagonal down and right.) We did not cover speed graphs this year, so don’t worry about
that part of the question.
15. What does at rest look like on a position graph, and on a speed graph?At rest on a position graph is a horizontal
line. This is because the y-axis has distance graphed on it, and if the line is horizontal that the distance is not
changing. Don’t worry about the speed graph.
16. What does constant speed look like on a position graph, and on a speed graph?Constant speed is any diagonal
line of constant slope. Don’t worry about the speed graph.
17. What does acceleration look like on a position graph, and on a speed graph?Acceleration is any curved line, or
any line that spot where this is a change in slope. Don’t worry about the speed graph.
18. What does an object do when there is net force acting on it?A net force causes an object to accelerate (speed
up, slow down, or change direction.) When the net force equals zero, then the object does not accelerate (stays
at rest or moving with a constant velocity.)
19. What force is needed to push a 4 kg object with an acceleration of 5 m/s2.F = m a. F = 4 x 5. F = 20 [N]
20. 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 arrive at the same time since they both fall with the same
acceleration of 9.81 [m/s2]
21. What is gravity, how much is it, and which way does it point?Gravity is a special type of acceleration. At the
surface of the Earth the value of gravity is 9.81 [m/s2].
22. What two things can an object do when the forces acting on it balance out?The object may remain at rest, or if
moving continue to move at a constant velocity.
23. What are the three things an object can do when there is a net force acting on it?An object may speed up, slow
down, or change directions.
24. 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
25. Find the speed of a cheetah that can run 24 meters in 2 seconds.v = Δd / Δtv = 24 / 12v = 2 [m/s]
26. Find the acceleration of a car that speeds up from 10 to 30 m/s in a time of 4 seconds.
a = Δv / Δt
a = 30 - 10 / 4
a = 20 / 4
a = 5 m/s2
27. Find how far a ball dropped from rest falls after 2 seconds.d = ½ a Δt2 d = ½ 10 22 d = 20 [m]
28. How are meteoroid, meteor, and meteorite different?Meteoroids are rocks that stay in space. Meteors are
rocks from space that burn up in the atmosphere. Meteorites are rocks from space that make it through the
atmosphere and land on the ground. You can only find meteorites on the surface of the Earth.
29. How does an asteroid differ from a comet?An asteroid is very large space rock, (like the size of a state). A comet
is a ball of ice, dust, and gasses. A comet also leaves a trail of gases behind it, so it looks like a comet has a tail.
30. Earth is special because it has lots of water. What percentage of the surface is covered in water and
land?Earth’s surface is 71% covered in water, and 29% covered in land.
31. What are two most common gasses in our atmosphere?Nitrogen at 78% and Oxygen at 21%. All the other
gasses like CO2, H2O and others together only make up 1% of the atmosphere.
32. List the three main services provided by the Earth’s atmosphere.The atmosphere provides a protective layer
from cosmic radiation, it smoothes out temperatures on the planet through wind, and it moves resources
around the planet (namely oxygen, carbon dioxide, and water).
33. 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 has very little atmosphere. Therefore it easy
to heat up, and there is no wind present to move the heat around and evenly distribute around the moon.
34. How long does it take the earth to rotate once, and what is this called?Earth rotates once each 24 hours. This is
called a day.
35. How long does it take the earth to revolve once around the sun, and what is this called?Earth revolves around
the sun once each 365.25 days. This is called a year.
36. How long does it take the moon to revolve once around the Earth, and what is this called?The moon revolves
around the Earth once every 29 days. This is called a lunar month. It used to be the regular month, until the
month was adjusted to add up to an exact year.
37. Explain why the Earth has seasons? Earth has seasons because it is tilted. The tilt of the Earth causes the
northern hemisphere to lean towards the sun in our summer, and to lean away from the sun in our winter.
38. What causes tides on Earth? When causes high tide to occur?The moon’s gravity pulls up on Earth’s water.
When the moon is directly over a body of water there is high tide there, and on the opposite side of the earth.
Low tide exists half way in-between two high tide times. For example if an area has a high tide at 8 PM and then
not again until 6 AM, the low tide occurred at 1 AM (which is exactly halfway in-between those two times.)
39. How is it possible to see the moon, even though it is not a star? The moon reflects sunlight that falls on it. This
makes the moon visible in the sky.
40. What happens in a lunar eclipse?A lunar eclipse occurs when the sun, earth, and moon are in a straight line and
the Earth casts a shadow on the moon.
41. What happens in a solar eclipse?A solar eclipse occurs when the sun, moon, and earth are in a straight line and
the moon casts a shadow on the Earth.
42. List the phases of the moon.New moon (0% lit), waxing crescent (1-49% lit), first quarter (50% lit), waxing
gibbous (51-99% lit), full moon (100% lit), waning gibbous (99-51% lit), last quarter (50% lit), waning crescent
(49-1% lit), and back to new moon (0% lit.) This cycle takes 29 days to complete.
43. What is the sun, what is it made out of?The sun is a ball of burning gases and flames. The sun is mostly made of
hydrogen and helium. It is a medium sized star, and it burns at medium temperature. This is why the sun is
orange in color. Larger stars that burn at higher temperatures look blue in color.
44. What is a light year? What does it mean to say something is 5 light years away?A light year is a unit of distance
that represents how far light travels in one year. This is a very large unit of distance when you think about it. If
something is 5 [Ly] away then it took the light 5 years to get to the observer. Put another way the observer sees
the image as it way 5 years ago. So looking at objects very far away in light years is a way to see what things
looked like in the past.
45. What is a solar system?A single star and the planets and moons that orbit it.
46. What is a constellation?A collection of solar systems.
47. What is a galaxy?A collection of constellations.
48. What is the Universe? A collection of all the galaxies. Universe is also considered to be all of space.
49. What is the reason for the different values of gravity on each planet in our solar system?The planets have
different values of gravity based on their mass and their size. The larger the mass the greater the gravity, and
the larger the size the smaller the gravity. This explains why Earth and Saturn have nearly the same amount of
gravity. Saturn has much more mass, but it is cancelled out by its increased size. Jupiter is also a giant of a
planet but it has so much more mass that it over comes the decrease in gravity for an increase in gravity over
Earth by about 3 times.
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Point to remember: Gravity depends on two things. The mass of the objects in question, and the distance
between the masses. The more mass means more gravity. The more distance means less gravity.
What does an H-R diagram show us about main sequence stars?H-R diagrams show that for main sequence stars
(most stars in the universe) the brighter the star the higher the temperature of the star.
How do you measure mass with a mass balance? You need to set up a see-saw system. Put the unknown mass
on one side, and put known masses on the other side until the system balances out. Then add up the known
masses for the mass of the unknown mass.
How balanced and set up, how do you use a triple beam balance? Start by sliding all the masses back to the zero
position. Then make sure the balance reads zero, (adjust with the know if needed.) Put the unknown mass on
the pan. Then slide the large mass to the last position that does not tip the scale. Then repeat with the medium
mass. Then slide the small mass to the spot that balances out the system. Add up the large, medium and small
masses for the mass of the unknown object.
How do you use an electronic scale to find the weight on an object in [N] and then the mass of the same object
in [g]? Turn on the scale. Select the unit you want. Press the tare button to zero out the scale. Put the object
on the pan. Read the weight of the object.
Calculate the volume of beaker with a height of 24 [cm] and a diameter of 8 [cm]. V = π r2 h. The radius is ½ of
the diameter. So r = 4. V = (π) (42 ) (24) = 1,206 cm3.
Calculate the volume of a box form Amazon.com that measure 60 [cm] by [24 cm] by [30 cm]. V = L W H.
V
3
= (60) (30) (24) = 43,200 cm .
Calculate the volume of a basketball that has a radius of 18 cm. V = (4/3) π r3. V = (4/3) π (183) = 24,429 cm3
What are the four properties of matter? What does each one measure? Mass: measure of matter and inertia,
Weight: measure of the force of gravity, Volume: measure of the amount space something takes up, and
Density: measure of the ratio of mass to volume.
Describe the method for finding the density of an object. Measure the mass of the object. Calculate the volume
of an object. Divide the mass by the volume for the density.
What is the density of a can of beans that has a mass of 450 [g] and a volume of 400 [cm3]. Does it sink, suspend
or rise in water?
What is the density of a can of whip cream that has a mass of 150 [g], and a volume of 500 [cm3]. Does it sink,
suspend or rise in water? D = m / V. D = 150 / 500 = 0.3 g/cm3. The object will rise in water since the density is
less than that of water.