for effects of forces on objects

1. Unit 5
2) Effects of FORCES
Learner’s book p. 119  p. 133
Workbook book p. 62  p. 68

2. Something that
cause an object
moves, changes its
speed, direction
and shape.
In science,
force, usually
means either a
push or a pull

3. B
A
D
J
F
H
I
C
G
E
K
L

4. What do you do to make a football move?
What do you do to make a moving ball move faster?
How does a goalkeeper stops a ball?
A hockey player changes the direction of ball with a flick of stick.

5. • In all these situations either the ball is made to move
faster or is slowed down or its direction is changed.
• Now the question arises what makes all these changes?

6. FORCE
A Force is a Push or Pull or both. A force cannot be seen but we can observe
the effect of force.
Push Pull
Push
and
Pull

7. •We cannot see forces.
• We can measure them and sometimes feel
the effects they have on things.
• Forces are measured in newtons (N)
Some Types of Force
Gravity
Friction
Air
resistance Upthrust
Weight

8. What do we call the force that makes
things fall to the ground on Earth?
The force of gravity also exists on the Moon
but it is not as strong as it is on the Earth.
This is because the Moon is much smaller than
the Earth.

10. Gravity
Gravity is a force that pulls objects
downwards towards the centre of the earth

11. MASS &WEIGHT
Mass : the amount of matter it contains
It is measured in grams (g) or kilograms (kg)
but it is NOT a force.
Weight : the force caused by gravity
pulling down on the mass of an
object.
It is measured in newtons (N).

12. EXAMPLES OF PUSH
Pushing a car
Pushing a
trolley
Rocket
launching
PUSH: Push is the applied force which intend to drive.

13. EXAMPLES OF PULL
Tug of war Pulling a trolley
Pulling body weight
PULL: Action which acts in direction of the origin of
force.

14. Examples of combination of Push
and Pull
Scrubbing the
floor Rowing the boat
Playing guitar

15. Effects of
Force
Changes the
shape
temporarily
Changes the
shape
permanently
Change the
direction of
moving object
Change the
speed of
moving object
Stops a
moving object
or makes a
stationary
object move

16. Change in the shape temporarily
Pressing a sponge Squeezing a spring
Stretching a
rubber band

17. Change in the shape permanently
Breaking of glass
Crushing a can

18. Change in the direction of moving
object
Change in the direction of ball

19. Change in the speed of object

20. Stops a moving object or makes a
stationary object move

21. RECAPITULATION
• Fill in the blanks:
1. To move a loaded trolley we have to it.
2. To stretch a bow we need to it.
• Tell whether objects are pushed or pulled in the following
cases:
Raising a flag
Pressing a switch
Knocking a nail

22. • What is the action of force on objects when
1.A lump of dough is pressed down with hands.
2. Pulling the free ends of a
rubber suspended from a hook.
3. Hammering a piece of iron.

24. Record Some objects’ mass and
Weight
No Objects Mass (g) Weight (N)
1 I 100 1
2 II 200 2
3 III 300 3
4 IV 400 4

25. Draw a line graph based on your
data
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
100 200 300 400
Weight
(N)
Mass (g)

26. Answer following question!
• 1. if the mass of an object is 560 grams, then how is it
weight?
• 2. if the weight of an object is 5 N, what is the mass of the
object?

27. Friction
What is Friction?
•Friction is the resistance between two
surfaces that are in contact with each other.

28. Which surface has greater friction?

29. Air Resistance
•Air resistance pushes against things which are
moving.

30. Streamlined shape
To cut through
the wind

31. Upthrust
Upthrust is the force that pushes an object up and makes it
seem to lose weight in a fluid. (Remember, a fluid means a
liquid or a gas)

32. When a force work on an object, there always another force
that work on it from the opposite site.
e.g:

33. Name the force showed by this
picture

34. Mass andWeight
• Mass is the amount of matter it contains
• Weight is the size of the force of the gravity depends on
the object’s mass and its distance from the object it’s
attracting.

35. How do we measure force?
• We measure force in newtons. We use an instrument called a
spring balance known as a force meter or a newton meter.

36. Experiment
I. Aim: Find out the different of force in the air and in the
water
II.Tools and materials
• Forcemeter
• Objects that sink in water (glass, plasticin, metal)
• water
• Jar

37. Prediction
• I predict that the weight of the object in the air will be
_(higher than, lower than or equal to) _ the weight of the
object in water. If I put more water into the beaker, I predict
that the reading on the Newton meter will __(increase,
decrease, or not be any different to before)

38. III. Procedures
• Attach an object to the forcemeter
• Check the force needed to lift it in the air
• Put the object on the water in the jar and make sure that its
not touch the bottom of the jar
• Record your data in a table
• Repeat your measurement for 3 times
• Do the same thing to other objects

39. IV.Table of force measurement
No.
Weight in
the air
(N)
Weight in the
water
(N)
Upthrust on object
(N)
I 4 0.5 4 – 0.5 = 3.5 N
II 4 1.5 4 – 1.5 = 2.5 N
III 4 1 4 – 1 = 3 N
Average 3 N
1. Plasticine

40. IV.Table of force measurement
No.
Weight in
the air
(N)
Weight in the
water
(N)
Upthrust on object
(N)
I 2 1.5 2 – 1.5 = 0.5 N
II 2 1.7 2 – 1.7 = 0.3 N
III 2 1.7 2 – 1.7 = 0.3 N
Average 0.37 N
2. Metal

41. V. Conclusion
• Is there any different when you measure the weight in the
air and in the water?_____
• Tell the difference___________
• What type of force that occurs in this experiment?

42. HOME ASSIGNMENT
• Give two examples each of situations in which you push
or pull to change the state of motion of objects.
• Give two examples of situations in which applied force
causes a change in the shape of an object.