Topic 4 - Forces and Energy Flashcards
How can energy of a system be changed
Mechanically (forces doing work), Electrically (by moving charge doing work), by heating or by radiation
How do you measure work done by a force
force x distance
What is work done
a force which does work over a distance
What does power mean
How much work is done per second
-It is the rate of energy transfer and is measured in Watts
How do you work out power
work done/ time taken
describe an example when work is done mechanically on an object and why is leads to a rise in temperature
A person pushing a box along a carpet
-work is done against frictional forces which transfers energy to kinetic store but also to the thermal store due to friction so overall temperature increases
Whats is the effect of a gravitational field on objects
non contact force- the gravittional attraction between objects is caused by their gravitational fields interacting
What is the effect of magnetic fields on objects
and electrostatic force
interacting magnetic fields cause attraction and repulsion between magnetic objects
-electrostatic force causes attraction and repulsion between electrical charges and their electric field
What are the forces that occur when objects are in contact with each other
both objects feel an equal and opposite force called an interaction pair (3rd law)
-these pairs can be shows with vectors (arrows diagram)
What is the resultant force
Overall force acting on an object
-at least 2 forces are acting on an object
How do you work out resultant forces on a straight line
adding those in same direction and subtracting any in opposite
Objects in equilibrium have a resultant force of…..
zero (this can be stationary or moving at constant speed)
Describe a situation where energy is transferred Mechanically (by doing work)
if a box is lifted off the floor work is done against gravity which causes energy to be transferred mechanically to objects kinetic and GPE stores
Describe a situation where energy is transferred electrially
electric ions carry charge electrically from mains power supply to thermal energy store of metal plates
Describe a situation where energy is transferred by heating
A pan of water on a stove-
energy is transferred by heating to thermal energy stores of pan and water
Describe a situation where energy is transferred by radiation
Toaster- coil of wire with high resistance heats and glows giving off infrared radiation and cooks the bread
What is a moment
The turning effect of a force
How do you calculate a moment
force x distance
How would someone get the maximum moment/turning effect
you could push at right angles as any other angle means smaller distance so smaller moment
What is the principle of moments for a an object in equilibrium
Sum of clockwise moments is = sum of the anticlockwise moments
What do leavers do
They make it easier to do work by transferring the turning effect by increasing the distance from the pivot where a force is applied
Explain how gears transmit rotational effects of forces
They fit together to transmit turning effects by interlocking,
a larger gear is slower but creates a large moment
a small gear is faster but has smaller moment
How can we work out speeds and moments of gears
gear ratios
