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Year 11
OCR
Higher

Terminal velocity

I can use the equation F = m × a to determine and explain the motion of falling objects.

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New
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Year 11
OCR
Higher

Terminal velocity

I can use the equation F = m × a to determine and explain the motion of falling objects.

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Share activities with pupils
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Lesson details

Key learning points

  1. An object that is dropped experiences a constant gravitational force towards the centre of Earth.
  2. For a falling object, drag acts in the opposite direction to the gravitational force.
  3. As a falling object speeds up, the air resistance pushing up on it increases.
  4. When the resultant force on a falling object becomes zero, the object reaches terminal velocity.

Keywords

  • Gravitational force - is a non–contact force that attracts objects with mass towards each other

  • Drag - is a force of a fluid on an object moving through it, in the opposite direction to the object’s motion

  • Resultant force - is the overall effect of the forces acting on an object

  • Terminal velocity - is the velocity of an object falling through a fluid, when there is zero resultant force

Common misconception

Pupils may believe that as air resistance increases, a falling object decelerates (slows down).

Analyse footage of a falling object played back in slow motion, or frame–by–frame, to show that the speed of a falling object increases, up to a maximum speed, and at no time does it slow down.

If time allows, the increase in terminal velocity with mass can be investigated by dropping paper bun–cases from about 2 m and measuring the average speed over the last 1 m of fall. Multiple bun cases stacked inside each other increase mass.
Teacher tip

Equipment

None required.

Content guidance

  • Risk assessment required - equipment

Supervision

Adult supervision required

Licence

This content is © Oak National Academy Limited (2024), 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.
Which of the following forces acts on all objects near Earth surface?
upthrust
friction
magnetic force
drag
Correct answer: gravitational force
Q2.
An aeroplane produces a horizontal forwards thrust of 3200 N and a drag force of 2400 N opposes the movement. What is the size of the resultant horizontal force acting on the aeroplane?
5600 N forwards
5600 N backwards
Correct answer: 800 N forwards
800 N backwards
0 N
Q3.
Which of the following is a statement of Newton’s Second Law of motion, using standard symbols?
$$v = x ÷ t$$
$$a = (v – u) ÷ t$$
Correct answer: $$F = m × a$$
$$m = F × a$$
$$a = F × m$$
Q4.
Five cars, A, B, C, D and E, travel along a straight road. There are three forces acting on each car, the values of which are listed below. Which of the cars are not accelerating?
Correct answer: car A: driving force = 500 N, air resistance = 300 N, friction = 200 N
car B: driving force = 600 N, air resistance = 300 N, friction = 200 N
car C: driving force = 700 N, air resistance = 300 N, friction = 300 N
car D: driving force = 800 N, air resistance = 300 N, friction = 400 N
Correct answer: Car E: driving force = 900 N, air resistance = 450 N, friction = 450 N
Q5.
What sized resultant force is needed to cause a lorry of mass 3000 kg to accelerate at 0.3 m/s$$^2$$?
0.3 N
100 N
Correct answer: 900 N
1000 N
10 000 N
Q6.
Calculate the acceleration of a skydiver of mass 70 kg with a weight of 700 N and a drag force of 490 N acting on them. You do not need to give the unit.
Correct Answer: 3, 3.0, 3.00, 3 m/s$$^2$$, 3.0 m/s$$^2$$

Exit quiz

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6 Questions

Q1.
Match the following key terms about terminal velocity to the correct description.
Correct Answer:gravitational force,non–contact force that attracts objects with mass towards each other

non–contact force that attracts objects with mass towards each other

Correct Answer:drag,the force of a fluid acting on an object moving through it

the force of a fluid acting on an object moving through it

Correct Answer:resultant force,the overall effect of the forces acting on an object

the overall effect of the forces acting on an object

Correct Answer:terminal velocity,the velocity of a falling object when there is no resultant force

the velocity of a falling object when there is no resultant force

Q2.
Which of the following statements about an object falling through the atmosphere are correct?
the object will continue to accelerate as there is only one force acting on it
Correct answer: the drag force increases as the speed of the falling object increases
the weight of the object increases as the speed of the object increases
Correct answer: at terminal velocity, the drag force is equal to the weight of the object
at terminal velocity, the drag force is greater than the weight of the object
Q3.
Five objects, A, B, C, D and E, are falling towards Earth. There are two forces acting on each object, the values of which are listed below. Which of the objects are at terminal velocity?
Object A: gravitational force = 40 N, drag force = 20 N
Object B: gravitational force = 200 N, drag force = 400 N
Correct answer: Object C: gravitational force = 200 N, drag force = 200 N
Object D: gravitational force = 200 N, drag force = 190 N
Correct answer: Object E: gravitational force = 0.4 N, drag force = 0.4 N
Q4.
A velocity–time graph for a falling object is shown. Match the labelled points to the correct descriptions.
An image in a quiz
Correct Answer:c,acceleration is zero: object has reached terminal velocity

acceleration is zero: object has reached terminal velocity

Correct Answer:a,acceleration is at its highest

acceleration is at its highest

Correct Answer:b,acceleration is at its lowest

acceleration is at its lowest

Q5.
A stone of mass 0.5 kg is falling in water. Its weight is 5.0 N and a drag force of 4.5 N is acting. Calculate the acceleration of the stone. You do not need to give the unit.
Correct Answer: 1, 1.0, 1.00, 1.0 m/s$$^2$$, 1 m/s$$^2$$
Q6.
Two balls, with the same diameter but different weights, are dropped from a height. Which two statements explain why the heavier ball reaches a higher terminal velocity then the lighter ball?
the drag force on the balls will be equal at their terminal velocities
Correct answer: the drag force increases with the speed of the falling objects
Correct answer: terminal velocity is reached when the drag force equals the weight
the weight of the balls changes as they fall
the heavy ball has a larger drag when it is at the same speed as the light ball