1. Seisen International School
Mr. Lee
Grade 7 Science
Tuesday, March 29, 2011

2. • Forces are pushes or pulls.
• Forces act in pairs. When things touch, there
are two forces acting in opposite directions.

5. The size of force
is measured in
newtons. You
can measure the
size of a force
with a forcemeter.
spring inside

6. Magnets produce forces that act upon each other. They
are called attraction and repulsion.

7. Mass vs. Weight
Grade 7 Science
Tuesday, March 29, 2011
Seisen International School

8. Does my mass change if
I leave Earth?
Mass –a measure of the
amount of matter in an object

9. How does my weight change on
different planets?
Weight – a measure
of the attraction between two objects
due to gravity

11. Location On Earth On the On In deep Near to a
Moon Jupiter space black
hole
Mass 100 kg 100 kg 100 kg 100 kg 100 kg
Too big to
Weight 1000 N 160 N 5400 N Almost measure.
nothing Gravity is so
big even
light is
pulled in.
Nothing
escapes a
black hole!

14. • Which of the following are measures of weight?
3/29/2011

15. Pushing Water Out of the Way
• When an object is put
into water, the height of
the water increases
• The object pushes water
out of the way
• The push up from the
liquid is called upthrust
• The upthrust force
depends on how much
liquid is pushed out of the
way Objects feel like they
weigh less in the
water.

16. • Some things are “light for
their size”
• Ex: cork, styrofoam, balsa
wood
• If the object floats, the
upthrust from the water is
equal to the weight of the
object
In your notebook, explain why • This means the density of
it is easier to float in the calm the object is less than the
ocean compared to a liquid.
freshwater lake.

17. • “How heavy something is
for its size”
• Density is a measure of
the amount of substance in
a given space.
• The formula for density is:
mass (g)
density 3
volume (cm )

18. Solve this one!
 Suppose a substance has a mass of 10
grams and a volume of 10 ml. What is
the density of this substance?
 1.0 g/ml
 This is the density of water

19. Anything with a
greater density
will sink!
Anything with a
lower density
will float!

20. Density Problem
• Oil, syrup,
water, 100
yen coin,
cork the left side of your notebook,
On
draw a big picture of a tall glass
showing what you think will happen
when we mix all of these things
together.

21. cork
oil
water
molasses
10 yen coin

22. • Predict what will happen when eggs
are dropped in normal water and in
salt water.

23. NEXT:
• Finish writing up a detailed explanation
(with drawings and color) of the straw and
colored liquid experiment that we did last
week.
• Mr. Lee will come around to stamp your
work when you are done.
• When you are done, complete the practice
questions on the next slide.

25. FRIICTTIIOn
FR C On
• Reducing Friction • Friction can be useful

26. FRICTION EXPERIMENT

27. M O V I N G AND STOPPING

32. Practice Questions
• Read pages 45 – 49
• Calculate the densities of the following:
1. Oil – 100cm3 of oil has a mass of 70 g
2. 25 cm3 of cork has mass of 3.75 g.
3. 50 ml of syrup has a mass of 55 g.
4. Does air have a density that is greater than or less
than 1.0 g/ml? Explain how you know this.

33. Grade 7 Science
Mr. Lee
Seisen International School
Tuesday, March 29, 2011

35.  Can you list 3 ways to reduce friction?
 Make surfaces smooth
 Put a lubricant on them
 Design the moving parts so that they roll on
each other rather than slide

36.  The friction force when
something slides through air or
liquid is called DRAG.

37.  Friction is used to
stop things moving.
 Car and bicycle
brakes!  friction is
increased
 Is a bald tire or a
new tire better at
gripping the road?
Why do we prefer
new tires?

38.  SPEED: tells you how
far you go in a certain
time
 What does 30 miles per
hour mean?
 The speed of a car
affects how long it
takes to stop: Write a
prediction about this
relationship.
 The faster you are
going, the longer it
takes for you to stop!
 *Brake pads use the
force of _________
to help stop the car

39. Turn to your neighbor and discuss the
chart above. Pretend to be a teacher
and a student.

40.  Use a meter stick ruler to determine if you have
a faster reaction time than your group
members.
 Do at least 5 trials and determine the average
of the trials.
 Compare the results with your other group
members.
 In your notebook, record the aim, results and
conclusion of your investigation.
 Answer these questions:
 What controlled variables were necessary in your
experiment to conduct a fair test on each participant?
 What could be a possible independent variable that
could affect someone’s reaction time.
 For additional points, carry out this experiment in the
remaining class time.

42. Write your name
on the piece of
paper and number
1 through 8.

43.  1.What season would it be in New York in
the picture shown?

44.  2.According to the picture, is it daytime or
nighttime in Japan?

45.  3.What season would it be right now in
Australia according to the picture?

46.  4.Name one part of the world that would be
experiencing VERY LONG DAYS in the diagram
below.

47. 5. How does the mass of a black
hole compare with the mass of
our sun?

48.  6.Explain why the Earth has
stronger gravity compared to the
moon.

49.  7.Study the diagram below carefully.
Explain why the beeswax floats in the water,
but sinks in the olive oil. Be detailed in your
answer.

50.  8. Eric and Sonya are shown in the picture with a
box. This question has two parts:
(a) what is causing the force pointing in the left
direction?
(b) if the arrows are the same length, what is
happening in the picture?