Chapter 36 - Force and Work Flashcards
What is (a) force? What can one cause an object to do?
A force is something that causes an object to accelerate.
Move faster, slow down, stop or change direction
Give an example of two forces balancing each other so neither is moving
A tug-of-war
What unit is used to measure force, and what instruments can be used to measure force
The Newton (N) A spring balance or Newton meter
List 5 different types of force, their effects and an example of each
Push - moves or increases speed or changed direction e.g. pushing a child on a swing
Pull - causes movement (as above) e.g. pulling off a boot
Weight - moves objects towards the centre of the earth e.g. a ball falling
Magnetic - moves magnetic materials e.g. picking up iron in a scrap yard
Electric - moves charged particles e.g. positive charge attracting negative
see page 268 of textbook for more
What causes weight?
The weight of an object is the force of gravity on it
How does weight vary on earth, in space and on the moon?
- on earth things weigh slightly less at the equator as it’s slightly further away from the centre of the earth than the poles
- the pull of the moon is about 6 times less than the pull of the earth, so objects on the moon would weigh around a sixth of what they’d weigh on earth
- deep in space, far from any planet, an object experiences no pull, so is weightless
What is mass measured in?
What is weight measured in?
M = Kg W = N
How would you calculate the weight of an object?
Mass (in kg) x 10 = Weight (in newtons)
What is friction?
Friction is a force which opposes motion between two objects in contact
List 3 disadvantages of friction
- It often slows things down - greater friction is often the main reason ships travel slower than planes
- Friction often results in waste of energy. In food mixers and car engines, for example, a lot of unwanted heat and sound energy is/are produced
- Friction wears away surfaces in contact with each other. Tyres lose their thread and brake pads on bicycles wear away due to constant contact
List 3 advantages of friction
- We use friction to stop or slow things down, e.g. the brakes of a car or bicycle use friction
- Friction between the tyres of a car and the road allow a car to move, and we need it to walk. Without a grip on the road, car wheels would just spin around
- Without friction you wouldn’t be able to pick up things with your fingers - writing would be almost impossible
List two lubricants and their specific uses
Oil/grease - used in engines to reduce friction between moving parts. Otherwise, very high temperatures would be created.
Synovial fluid - acts as an lubricant in our joints
What is Hooke’s law?
The extension of a spring is directly proportional to the force that’s stretching it
When is work said to be done in physics?
When a force moves an object, e.g. swimming or writing
How do we calculate the amount of work done?
Force x Distance Moved = Work Done
By multiplying the applied force by the distance that the object moves
What unit is used to measure work done?
The joule (J)
What is energy, and what unit is used to measure it?
Energy is the ability to do work The joule (J)
What is power?
Power is a measure of how quickly work is done - the rate of doing work or the work done by unit time
What unit is used to measure power, and what else is it?
It is also energy used per second, and is measured in watts.
e.g. a 100W bulb uses 100J of energy each second
What is power? (DEFINITION TIME)
Power is the work done per unit time
OR
Power = work done/time taken, so work done divided by time taken
