FORCES IN ACTION

FORCE

Something that cause an object moves, changes its speed, direction and shape.

In science, force, usually means either a push or a pull

B A

D

J

F

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I

C

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E

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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

What do we call the force that makes things fall to

the ground on Earth?

GRAVITY

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.

GravityGravity is a force that pulls objects downwards towards the centre of the earth

MASS & WEIGHT

Mass : the amount of matter it containsIt 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).

Record Some objects’ mass and Weight

No Objects Mass (g)

Weight (N)

1 I 100 12 II 200 23 III 300 34 IV 400 4

Draw a line graph based on your data

100 200 300 4000

0.5

1

1.5

2

2.5

3

3.5

4

4.5

Mass (g)

Weig

ht

(N)

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?

FrictionWhat is Friction?

Friction is the resistance between two surfaces that are in contact with each other.

Which surface has greater friction?

Sport car circuit

Air Resistance

Air resistance pushes against things which are moving.

Streamlined shape

To cut through the wind

Which surface has greater friction?

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)

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

e.g:

push

Air

resistance

Name the force showed by this picture

Mass and Weight

Mass is the amount of matter it containsWeight is the size of the force of the gravity depends on the object’s mass and its distance from the object it’s attracting.

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.   

Experiment

I. Aim: Find out the different of force in the air and in the water

II. Tools and materialsForcemeterObjects that sink in water (glass, plasticin, metal) water Jar

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)

III. Procedures

Attach an object to the forcemeterCheck the force needed to lift it in the airPut the object on the water in the jar and make sure that its not touch the bottom of the jarRecord your data in a tableRepeat your measurement for 3 timesDo the same thing to other objects

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

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

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?