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Year 11
AQA
Foundation

Resultant forces and their effects

I can determine the change of motion caused by one dimensional forces acting on an object.

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Year 11
AQA
Foundation

Resultant forces and their effects

I can determine the change of motion caused by one dimensional forces acting on an object.

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Lesson details

Key learning points

  1. A single resultant force has the same effect as several forces acting on an object
  2. If there is no resultant force on an object, it remains still or continues to move at a steady speed in a straight line
  3. If there is a resultant force on an object, it will accelerate in the direction of the force
  4. A resultant force acting in the opposite direction to movement will decelerate (slow down) an object

Keywords

  • Resultant force - the effect of a set of forces on an object

  • Newton’s First Law of motion - an object will remain at rest, or in motion in a straight line at constant speed, unless there is a resultant force acting on it

  • Velocity - the rate of change of displacement of an object, measured in metres per second (m/s)

  • Accelerate - a change in the speed and/or direction of an object

  • Decelerate - a decrease in the speed of an object

Common misconception

A common belief is that a resultant force is needed to keep an object in motion, and if no resultant force acts on an object then it must be stationary.

Discuss examples in which friction is very low or absent, such as a puck sliding across an ice rink or an object being dropped during a space walk and extrapolate to what would happen if friction disappeared entirely.


To help you plan your year 11 physics lesson on: Resultant forces and their effects, download all teaching resources for free and adapt to suit your pupils' needs...

A linear air track, or air hockey table, is an excellent way of showing that objects will move at a constant speed if friction can be eliminated. Try to show this motion to convince pupils that Newton's First Law is valid for moving objects as they can struggle to accept this.
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This content is © Oak National Academy Limited (2025), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Lesson video

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Starter quiz

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6 Questions

Q1.
How many newtons (N) are there in 2.5 MN?
2500
25,000
250,000
Correct answer: 2,500,000
25,000,000
Q2.
When two or more forces act on an object, we can imagine a single force that has the same effect as this combination of forces. This single force is called the force.
Correct Answer: resultant, net
Q3.
A coin is dropped into a swimming pool. While the coin is falling downwards through the water, which of the following forces act on it?
air resistance
Correct answer: gravitational force
normal reaction force
Correct answer: drag
Q4.
There is a law of physics which states that forces come in equal and opposite pairs, which act between pairs of objects. What is the name of this law?
Newton’s First Law of motion
Newton’s Second Law of motion
Correct answer: Newton’s Third Law of motion
Newton’s Fourth Law of motion
Q5.
Which of the following are correct definitions of acceleration?
change in displacement divided by time taken
Correct answer: rate of change of velocity
time taken to change velocity by one metre per second
Correct answer: change in velocity per second
Q6.
Which of the following situations involve a change in velocity?
Correct answer: A car increases speed as it travels in a straight line.
A car travels in a straight line at a steady speed.
Correct answer: A car turns a corner without changing speed.
Correct answer: A car slows down while turning a corner.

Exit quiz

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6 Questions

Q1.
The diagram shows four forces acting on an object. What is the magnitude of the resultant force?
An image in a quiz
Correct answer: 1 N
5 N
6 N
7 N
13 N
Q2.
Which of the following is not caused by a resultant force acting on an object?
Correct answer: moving at constant velocity
changing direction
start moving
stop moving
decelerating and changing direction
Q3.
Which of the following statements are included in Newton’s First Law of motion?
Correct answer: A stationary object remains stationary if there is no resultant force.
Every action has an equal and opposite reaction.
Correct answer: A moving object’s velocity stays the same if no resultant force acts.
When object A exerts a force on object B, B also exerts a force on A.
Q4.
A ship travels at a constant speed without changing direction. Which of the following statements are correct?
There is a steady resultant force acting on the ship.
Correct answer: There is no resultant force acting on the ship.
Correct answer: The force pushing it forwards is equal to the force pushing it backwards.
The force pushing it forwards is greater than the force pushing it backwards.
Q5.
A person pushes a stone across a frozen lake. After they let go, the stone slides across the ice, slowing and stopping before it reaches the other side of the lake. Why does the stone slow and stop?
The person’s pushing force runs out.
The person’s pushing force transfers to the thermal store.
Correct answer: There is a resultant force acting in the opposite direction to the motion.
Other forces cancel out the person’s pushing force.
Q6.
Which of the following vans is decelerating?
Correct Answer: An image in a quiz
An image in a quiz
An image in a quiz
An image in a quiz
An image in a quiz