Starter quiz
- Which of the following forces acts on all objects near Earth surface?
- upthrust
- friction
- magnetic force
- drag
- gravitational force ✓
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- 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
- 800 N forwards ✓
- 800 N backwards
- 0 N
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- Which of the following is a statement of Newton’s Second Law of motion, using standard symbols?
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- ✓
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- 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?
- 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
- car E: driving force = 900 N, air resistance = 450 N, friction = 450 N ✓
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- What sized resultant force is needed to cause a lorry of mass 3000 kg to accelerate at 0.3 m/s?
- 0.3 N
- 100 N
- 900 N ✓
- 1000 N
- 10 000 N
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- 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.
- '3' ✓
Exit quiz
- Match the following key terms about terminal velocity to the correct description.
- gravitational force⇔Non–contact force that attracts objects with mass towards each other. ✓
- drag⇔The force of a fluid acting on an object moving through it. ✓
- resultant force⇔The overall effect of the forces acting on an object. ✓
- terminal velocity⇔The velocity of a falling object when there is no resultant force. ✓
- 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.
- 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.
- 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.
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- 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
- object C: gravitational force = 200 N, drag force = 200 N ✓
- object D: gravitational force = 200 N, drag force = 190 N
- object E: gravitational force = 0.4 N, drag force = 0.4 N ✓
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A graph of the velocity-time for a falling object is shown. Match the labelled points to the descriptions.- c⇔no resultant force: object has reached terminal velocity ✓
- a⇔resultant force is high ✓
- b⇔resultant force is low ✓
- 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.
- '1' ✓
- 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.
- The drag force increases with the speed of the falling objects. ✓
- 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.
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Worksheet
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Video
Lesson Details
Key learning points
- An object that is dropped experiences a constant gravitational force towards the centre of the Earth
- For a falling object, air resistance acts in the opposite direction to the gravitational force
- As a falling object speeds up, the air resistance pushing up on it increases
- When the resultant force on a falling object becomes zero, the object reaches terminal velocity.
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.
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
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