A force is a push or pull that can change an object's motion. When forces acting on an object are balanced (equal in size, opposite in direction), the object's motion doesn't change — it stays still or keeps moving at a steady speed in a straight line. When forces are unbalanced, the object's motion changes — it speeds up, slows down, or changes direction. The bigger the unbalanced (net) force, the bigger the change in motion, and heavier objects (more mass) need more force to achieve the same change in motion as lighter ones. Gravity is a constant force pulling objects toward Earth.
Example
A book resting on a table has balanced forces — gravity pulling it down is exactly matched by the table pushing up. But when you push a shopping trolley, your push force is greater than friction, so the forces are unbalanced and the trolley speeds up.
Key terms
Balanced forces:
Forces that are equal in size and opposite in direction, causing no change in motion.
Unbalanced forces:
Forces that are unequal, causing a change in an object's motion.
Net force:
The overall force after combining all forces acting on an object.
Questions
1. A force is:
A type of energy only
A push or a pull
A colour
A type of matter
2. Balanced forces are:
Unequal in size
Equal in size and opposite in direction
Always zero
Always in the same direction
3. When forces are balanced, an object's motion:
Always speeds up
Doesn't change
Always stops
Always reverses
4. Unbalanced forces cause:
No change at all
A change in motion
Only heat
Nothing
5. Gravity is a force that:
Pushes objects away from Earth
Pulls objects toward Earth
Only affects light objects
Doesn't exist
6. A book resting still on a table has forces that are:
Unbalanced
Balanced
Absent
Random
7. The net force is:
Only the pushing force
The overall force after combining all forces
A type of gravity
Always zero
8. Pushing a trolley so it speeds up means the forces are:
Balanced
Unbalanced
Absent
Equal
9. A car travelling at a constant speed in a straight line has forces that are:
Unbalanced
Balanced
Random
Absent
10. A bigger unbalanced force causes:
A smaller change in motion
A bigger change in motion
No change at all
Only a colour change
11. A heavier object needs ___ force to achieve the same change in motion as a lighter one.
Less
More
No
Random amounts of
12. If you push a box and it doesn't move, the forces acting on it are likely:
Unbalanced, causing motion
Balanced, since friction matches your push
Nonexistent
Always in your favour
13. A skydiver falling at a constant speed (not speeding up) has reached a point where:
Gravity is much stronger than air resistance
Gravity and air resistance are balanced
There are no forces acting
Gravity has stopped
14. Which scenario shows unbalanced forces?
A parked car
A book on a table
A ball rolling to a stop due to friction
Two people pushing equally on opposite sides of a box
15. A rocket accelerates upward because:
Its thrust force is less than gravity
Its thrust force is greater than gravity
All forces are balanced
There is no gravity in the atmosphere
16. Two teams in a tug of war pull with exactly equal force. The rope:
Moves toward the stronger team
Stays still, since forces are balanced
Moves randomly
Breaks immediately
17. Why does a feather fall slower than a rock in air, even though gravity pulls on both?
Gravity is weaker on feathers
Air resistance has a much greater relative effect on the lighter, larger-surface-area feather
Feathers are not affected by gravity at all
Rocks are affected by less gravity
18. An object moving at a constant velocity (steady speed, straight line) must have:
No forces acting on it at all
Balanced forces acting on it
Only gravity acting on it
Constantly changing forces
19. If you know an object is accelerating, what can you conclude about the forces acting on it?
The forces must be balanced
The forces must be unbalanced
There must be no forces at all
Nothing can be concluded
20. Understanding balanced and unbalanced forces mainly helps explain:
Why objects never move
Why and how objects speed up, slow down or change direction
Only why objects are heavy
Colours of objects
Answer key (parent copy)
1. A push or a pull
2. Equal in size and opposite in direction
3. Doesn't change
4. A change in motion
5. Pulls objects toward Earth
6. Balanced
7. The overall force after combining all forces
8. Unbalanced
9. Balanced
10. A bigger change in motion
11. More
12. Balanced, since friction matches your push
13. Gravity and air resistance are balanced
14. A ball rolling to a stop due to friction
15. Its thrust force is greater than gravity
16. Stays still, since forces are balanced
17. Air resistance has a much greater relative effect on the lighter, larger-surface-area feather
18. Balanced forces acting on it
19. The forces must be unbalanced
20. Why and how objects speed up, slow down or change direction