1. BALANCED AND
UNBALANCED FORCES

2. Balanced and unbalanced forces
In this section you will
review the forces work you covered in ks 3
learn how balanced and unbalanced forces
affect the motion of an object
Use the rules to work out how objects are
moving

3. KEY IDEAS
When two equal forces act on an object in opposite
directions we say that the forces are There
is no overall force on the object so it does not .
When the size of the forces are different we say that
the forces are There overall force is
called a force so the object

4. KEY IDEAS
When two equal forces act on an object in opposite
directions we say that the forces are balanced. There
is no overall force on the object so it does not
accelerate.
When the size of the forces are different we say that
the forces are unbalanced. There overall force is
called a resultant force so the object accelerates.

5. USING THE RULES

6. Four common types of force are:
LIFT, THRUST, DRAG and WEIGHT
Look at the following situations and
see if you can identify the correct forces
in each example

7. Name each of the forces shown by the arrows arrows.
1 A person
falling at their
terminal velocity
Click for help
Weight
Drag
Thrust
lift
4 A plane flying
horizontally
at a steady speed
2 A falling person
who has just opened
their parachute
5 A plane
accelerating
and
taking
off
3 A car travelling at it’s top speed

8. Answers 1 A person falling at their terminal velocity 4 A plane flying
horizontally
at a steady speed
2 A falling person
who has just opened
their parachute
5 A plane
accelerating
and
taking
off
3 A car travelling at it’s top speed

9. ANSWERS
with
explanations

10. 1
A person falling
at their terminal
velocity
Drag
Weight
Terminal velocity tells us that there is
no so the forces are

11. 1
A person falling
at their terminal
velocity
Drag
Weight
Terminal velocity tells us that there is
no so the forces are

12. 2 A falling person who has just opened their parachute Drag Weight
Opening the parachute will the person
down ( ). The forces are

13. 2 A falling person who has just opened their parachute Drag Weight
Opening the parachute will slow the person
down (deceleration). The forces are unbalanced

14. 3
A car travelling
at it’s top speed
Top speed tells us that there is
so the forces are
Drag
Thrust

15. 3
A car travelling
at it’s top speed
Top speed tells us that there is
so the forces are
Drag
Thrust

16. Lift 4
A plane flying
horizontally at
a steady speed
Thrust
Drag
tells us that
the weight the lift
Weight
tells us that
the thrust the drag

17. Lift 4
A plane flying
horizontally at
a steady speed
Thrust
Drag
Horizontal tells us that
the weight balances the lift
Weight
Steady speed tells us that
the thrust balances the drag

18. Steady speed Speeding up LIFT THRUST DRAG WEIGHT Click to take off
and watch the size
of the force arrows
THRUST
DRAG
Steady speed
Speeding up
WEIGHT

19. Lift 5
A plane
accelerating
and taking off
Thrust
drag
tells
us that the thrust is bigger
than the drag
weight
tells us that
the lift is greater than the weight

20. Lift 5
A plane
accelerating
and taking off
Thrust
drag
Accelerating tells
us that the thrust is bigger
than the drag (unbalanced)
weight
Taking off tells us that
the lift is greater than the weight (unbalanced)

21. Isaac Newton said that:-
Objects that are stationary or moving at a
velocity will have no resultant
acting on it.
Objects whose is changing will have
a force acting on them. They will be
accelerating or

22. END Isaac Newton said that:-
Objects that are stationary or moving at a
constant velocity will have no resultant force
acting on it.
Objects whose velocity is changing will have
a resultant force acting on them. They will be
accelerating or decelerating.
END