1. Effects of Force

2. What is a Force?
Forces have both a size and a direction, and they usually work in pairs.
For example, there are two forces at work when you swim: your body pushes down on the water, and the water pushes your body up so you don’t sink to the bottom.
Forces are measured in newtons (N), using a forcemeter.
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3. Effects of Force
Forces stop or start an object moving, or change its direction. They can also change an object’s shape.
Forces are needed in the following everyday examples:
to steer a car round a corner;
to stretch an elastic band;
to push a door open.
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4. Question 1 Which of the following can be an effect of a force?
A) A change of movement
B) A change in color
C) A change in material
D) None of the above

5. Effects of Force
When a box rests on a flat surface, the weight W (a force) of the object pushes down from the center of the box.
Weight
Normal
The box does not move because the normal force N exerted by the surface of the table is equal and opposite to the weight of the box.
When an object is at rest (stationary), or moving in a straight line at a constant speed, the forces acting on the object are balanced.
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6. Effects of Force
If the forces acting on an object become unbalanced - because there is greater force in one direction than another - the motion of the object will change.
Balanced
The overall effect of all forces acting on an object is known as the net force.
Unbalanced
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7. Question 2
The force acting on the box in the diagram is unbalanced. Which of the following options could make the forces acting on the object balance?
A) A force of equal size pushing down from the top. A
B) A force of equal size pushing up from the bottom.
Force C
C) A force of equal size pushing from the right. D B
D) Another force of equal size pushing from the left, alongside the original force.

8. Types of Force Forces can be divided into contact and field forces.
Contact Forces:
These are forces that involve physical contact between two objects.
Examples include the force exerted by the wind on a boat sail or by our feet on the floor.
Field Forces:
These are forces that act at a distance, with no physical contact between the objects.
Examples include the forces of gravity and magnetism.
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9. Weight (gravitational force)
Everyday Types of Forces
Weight (gravitational force)
There are many forces which we experience every day:
Gravitational Force (weight): This is the force with which an object, such as the Earth or the Moon, attracts other objects towards itself. It is a downward force, always equal to the weight of the object.
(Note that weight is not the same as mass, which is measured in kilograms with a balance.)
Have you ever heard the saying, “what goes up must come down”?
The gravity of the Earth pulls objects towards itself. This is why, when you throw a ball up in the air, it always comes back down. Without gravity, the ball would keep going up in a straight line forever (unless acted upon by different force).
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10. Everyday Types of Forces
Other common forces are:
Applied force
Applied Force: An applied force is a force which is applied to an object by another object or by a person. A push or a shove, for example.
Frictional force
Friction: The force that resists the movement of two surfaces touching each other.
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11. Weight (gravitational force)
Everyday Types of Forces
Normal Force: The normal force supports an object that is in contact with another object.
Normal
Weight (gravitational force)
When you lean on a wall, the normal force stops the wall from bending under your weight.
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12. Everyday Types of Forces
Air Resistance is a special type of friction which acts upon objects as they travel through the air.
Tension is the force which acts on a string, rope, or wire when it is pulled tight by forces acting at each end.
Compression is a force which tries to squash an object.
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13. Question 3 Which of the following is NOT a contact force? A) Tension
B) Gravity
C) Friction
D) Compression

14. Question 4
When you push a door open, what type of force are you exerting on the door?
A) Gravitational force
B) Applied force
C) Tension
D) Compression

15. Assessment Q1 What is net force?
When the forces acting on an object are balanced.
When the forces acting on an object are unbalanced.
The sum of all forces acting on an object.
A pulling force.

16. In which of the following situations is NO net force being exerted?
Assessment Q2
In which of the following situations is NO net force being exerted?
A car turning left
A ball moving in a straight line at a constant speed.
An ice skater slowing down
A ball bouncing off a wall.

17. Which of the following best describes field forces?
Assessment Q3
Which of the following best describes field forces?
Forces that cause an object to change position
Forces that cause an object to change shape
Forces that involve physical contact between two objects.
A ball bouncing off a wall

18. Assessment Q4
What is the relationship between force applied to a spring and the change of extension of that spring?
It depends on what the spring is made of
The relationship is proportional
As the force applied increases, the extension of the spring decreases.
There is no relationship

19. Which force is always equal to the weight of an object?
Assessment Q5
Which force is always equal to the weight of an object?
Friction
Tension
Gravitational Force
Air resistance

20. Which of the following could be a contact force?
Assessment Q6
Which of the following could be a contact force?
Applied force
Gravity
Magnetism

21. Assessment Q7
Which force can support an object that is in contact with another object?
Applied force
Gravitational Force
Normal Force
Magnetic Force

22. Assessment Q8
Choose the option that best completes the following statement: Compression makes an object…
Change direction.
Bigger.
Shorter.
Longer.

23. Assessment Q9
The forces acting on an object are balanced when the object is at rest. In which of the following cases are the forces acting on an object also balanced?
When the object is changing direction and accelerating.
When the object is moving in a straight line and accelerating.
When the object is changing direction at a constant speed.
When the object is moving in a straight line at a constant speed.

24. What is the unit of measurement for force?
Assessment Q10
What is the unit of measurement for force?
Meters per second
Newtons
Kilograms
Joule