Friction opposes the relative motion between surfaces and starting a stationary object takes more force than sliding it, so this Grade 8 sheet opens with the two friction behaviour rules. Lubricants and static friction are given as ways to reduce and name friction.
Key Takeaways
Friction opposes the relative motion between surfaces (Q1).
Starting a stationary object needs a greater force than sliding it (Q2).
Q4 records using lubricants to reduce friction.
Section A: Multiple Choice Questions (1 Mark Each)
Choose the correct option for each question.
1.Friction is a force that:
(a) Helps the motion of objects(b) Opposes the relative motion between surfaces(c) Always increases speed(d) Acts only in air
2.The force required to start moving a stationary object is:
(a) Equal to sliding friction(b) Greater than sliding friction(c) Less than sliding friction(d) Zero
3.Which of the following surfaces produces the least friction?
(a) Sandpaper(b) Wood(c) Glass(d) Cement
4.Friction can be reduced by:
(a) Using lubricants(b) Making surfaces rougher(c) Increasing the force of contact(d) All of these
5.Which type of friction is the largest in magnitude?
(a) Static friction(b) Sliding friction(c) Rolling friction(d) Fluid friction
6.Rolling friction is ____ than sliding friction.
(a) Greater(b) Smaller(c) Equal(d) Unrelated
Section B: Short Answer Type Questions (2 Marks Each)
Show all steps clearly.
7.Define friction. On what two factors does the force of friction depend?
8.Why do athletes use shoes with spikes?
9.How does lubrication reduce friction? Give an example.
10.Why is rolling friction less than sliding friction?
11.What is fluid friction? Why do ships and aeroplanes have streamlined shapes?
12.Why do kabaddi players rub their hands with soil before a match?
13.Why does a matchstick light up when it is rubbed against the side of a matchbox?
14.Is friction useful or harmful? Give one example each of a useful and a harmful effect of friction.
Section C: Numericals & Word Problems (3 Marks Each)
Apply the concepts to solve the problems. Show all working.
15.A force of 50 N is applied to push a box, but a frictional force of 20 N opposes its motion. Find the net force acting on the box.
16.A 5 kg block is dragged with a force of 30 N and moves with constant velocity. What is the magnitude of the force of friction acting on it?
17.A ball rolling on the ground comes to rest after some time. Name the force responsible and explain why the ball stops.
18.A car moving at 20 m/s is stopped by applying brakes. If the frictional force produces a deceleration of 2 m/s², how long will the car take to stop?
19.A 10 kg box is at rest on a floor. The maximum static friction is 40 N. A horizontal force of 35 N is applied. Will the box move? Justify.
20.Why is it easier to move a heavy cart when it is fitted with wheels than when it is dragged along the ground?
Answer Key
1. b) Opposes the relative motion between surfaces
2. b) Greater than sliding friction
3. c) Glass
4. a) Using lubricants
5. a) Static friction
6. b) Smaller
7. Refer to solution guide.
8. Refer to solution guide.
9. Refer to solution guide.
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11. Refer to solution guide.
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20. Refer to solution guide.
End of Worksheet
People Also Ask
What does friction oppose?
The relative motion between surfaces, option (b) in this worksheet (Q1).
What force is needed to start a stationary object?
A force greater than sliding friction, option (b) in this worksheet (Q2).
How can friction be reduced?
Using lubricants, option (a) in this worksheet (Q4).
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