Force, Work and Power Flashcards
What is force measured in?
Newtons (N)
What is a force?
A force is any thing which can change the velocity of an object or make it move.
Finish the sentence.
For every force…
an equal but opposite force is exerted
What is friction?
Friction is a force which prevents the easy movement between two objects in contact.
What can force be measured using?
a spring balance
What is a law to do with force?
What does it state?
Hooke’s Law states that the extension of a spring depends on the force pulling on it (e.g. the weight of a mass attached to the spring).
What is work?
Work is done when a force moves an object.
What is work measured in?
Joules
State the equation used to find work
Work(J) = Force(N) X Distance(M)
What is power?
The rate at which work is done
What is power measured in?
watts
what is one watt in joules?
1 joule per second
write in words a formula for the average power.
The average power (watts) is the work done (joules) divided by the time taken (seconds).
Write out a formula for power
Power = Work done
—————
Time taken
What is velocity?
Speed in a given direction
Name 6 examples of forces
Pushing, pulling, twisting, friction, weight, gravity
Name 4 benefits of friction
To stop things slipping. e.g A car doesn’t slip on a corner because of friction.
To stop a bicycle (friction between the brake pad and the wheel.)
To use a nail; it grips whatever it is drilled into, therefore using friction.
To let us walk without slipping. (friction between your feet and the ground
when you take a step)
Name 4 disadvantages of friction
Friction causes blisters when your skin rubs off your shoe.
When you drive there is friction between the air and the car. This
wastes fuel.
Friction between the gases in the atmosphere and a space shuttle can
cause it to overheat upon re-entry. This can have disastrous
consequences.
Friction causes things to wear away; for instance the sole of your shoe
after you have been walking for a while.
Name 3 ways of preventing friction.
The use of lubricants like…
Oil and grease in cars to stop things
wearing away and/or heating up.
Our joints are surrounded by a fluid that
acts as a lubricant to reduce friction.
When you lubricate the hinges on doors
it can stop them squeaking as it
reduces friction.
A force of 10 N is being used to move an object a distance of 20 metres. Calculate the work done.
Answer = Work = Force by Distance
10 N X 20
Work = 200 Joules
Calculate the work done when a force of 15 N moves an object a distance of 40 cm.
When calculating the work done it is important that the distance is measured in metres. In this question we change 40cm to 0.4m.
Work = Force X Distance Work = 15 N X 0.4m Work = 6J
A weightlifter lifts 120 kg through a height of 2 m. Calculate the work done.
When lifting objects vertically the force needed is equal to the weight of the object.
Weight = Mass X 10 Force = 120kg X 10 Force = 1200 N Therefore calculate the work use: Work = Force X Distance Work = 1200 N X 2m Work = 2400 J
A force of 10 N is being used to move an object a distance of 20m in a time of 5 s. Calculate the value of average power.
Work done = Force X Distance
= 10 N X 20 m
= 200 J
Power = Work
--------
Time
Power = 200 J
--------
5 s
Power = 40 watts
A weightlifter lifts 120 kg through a height of 2 m in a time of 3 s. Calculate the average power developed.
We saw earlier
Work done = Force X Distance
= Weight X Distance
= 1200 N X 2 m
= 2400 J
Power = Work
——-
Time
Power = 2400 J
———–
3 s
Power = 800 watts
