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Year 11
OCR
Higher

Forces in two dimensions

I can draw and interpret free body force diagrams to describe the resultant force on an object.

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New
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Year 11
OCR
Higher

Forces in two dimensions

I can draw and interpret free body force diagrams to describe the resultant force on an object.

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Lesson details

Key learning points

  1. A free body diagram shows all of the forces acting on a single object.
  2. The resultant of two forces can be determined by adding individual forces on a vector diagram.
  3. The resultant of two perpendicular forces is in a different direction from either of these forces.

Keywords

  • Resultant force - A single force that represents the effect of all the forces acting on an object.

  • Equilibrium - The state of an object if there is no resultant force acting on it.

  • Vector diagram - A drawing in which forces are drawn end–to–end, and to scale, which can be used to find a resultant force.

Common misconception

The velocity of an object must be in the same direction as the resultant force acting on the object.

Invite pupils to consider situations in which the resultant force is not in the same direction as the velocity, such as an object that has been thrown upwards and is slowing down as its height increases.

Pupils should use 1 cm squared paper to draw a range of forces to find a resultant; trigonometric techniques are not required. However, the 'parallelogram of forces' technique can be used instead of 'joining forces end–to–end' if preferred.
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Teacher tip
equipment-required

Equipment

1 cm squared paper.

copyright

Licence

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 53 kN?
5300 N
Correct answer: 53 000 N
530 000 N
53 000 000 N
Q2.
The diagram shows a force arrow drawn on a grid of 1 cm squares. What is the magnitude of the force?
An image in a quiz
left
right
3 N
6 N
Correct answer: 12 N
Q3.
There is a law of physics which states that an object will remain at rest, or in motion in a straight line at constant speed, unless a resultant force is acting on it. What is the name of this law?
Correct answer: Newton’s First Law of motion
Newton’s Second Law of motion
Newton’s Third Law of motion
Newton’s Fourth Law of motion
Q4.
What is the magnitude of the resultant force in the diagram shown?
An image in a quiz
Correct answer: 203 N
248 N
253 N
293 N
Q5.
The diagram shows an object with a single force acting on it. Which of the following are possible descriptions of the object’s motion?
An image in a quiz
The object is moving to the left at constant speed.
The object is moving to the right at constant speed.
Correct answer: The object is accelerating.
Correct answer: The object is decelerating.
Q6.
A child throws a ball straight up. Which of the following is a correct free body diagram of the ball as it travels upwards?
An image in a quiz
An image in a quiz
An image in a quiz
Correct Answer: An image in a quiz
An image in a quiz

Exit quiz

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6 Questions

Q1.
Which of the following does an object in equilibrium never do?
move
stay still
Correct answer: start moving
Correct answer: accelerate
Correct answer: change direction
Q2.
A duck is swimming in a straight line across the surface of a lake, at a steady speed. Which of the following free body diagrams correctly shows the forces acting on the duck?
An image in a quiz
An image in a quiz
Correct Answer: An image in a quiz
An image in a quiz
An image in a quiz
An image in a quiz
Q3.
A helicopter is in equilibrium in the air. Which of the following motions are possible?
Correct answer: It is moving upwards at constant speed.
It is falling with decreasing speed.
It is travelling in a circle.
Correct answer: It is stationary.
Q4.
An aeroplane and its free body diagram are shown. Which of the following are possible descriptions of the aeroplane’s motion?
An image in a quiz
Correct answer: Moving to the left at decreasing speed.
Moving downwards at increasing speed.
Moving up at increasing speed, while also moving steadily to the right.
Correct answer: Moving to the left at decreasing speed, while also moving steadily upwards.
Correct answer: Moving to the left at decreasing speed, while also moving steadily downwards.
Q5.
A spaceship in space uses two rockets to produce forces acting in two directions at the same time. Which of the following vector diagram shows how to find the resultant force?
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An image in a quiz
An image in a quiz
An image in a quiz
Correct Answer: An image in a quiz
An image in a quiz
Q6.
The vector diagram shows the addition of three forces to find the resultant force. What is the magnitude of the resultant force?
An image in a quiz
Correct answer: 40 N
60 N
63 N
72 N