2. • Forces are pushes or pulls.
• Forces act in pairs. When things touch, there
are two forces acting in opposite directions.
3.
4.
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
10.
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!
12.
13.
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.
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.
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
34.
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.
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?
