2.2 - Energy Flashcards
What is gravitational potential energy (E little p in bottom corner)
The energy the object has by virtue of its position in a gravitational field
What is kinetic energy (E little k in bottom corner)
It’s the energy an object has by virtue of its movement
Tell me about transfers between kinetic and gravitational energy
As objects rise or fall, gpe can be converted to kinetic energy and kinetic energy can be converted to gravitational potential energy
How can gpe be calculated
Gpe (J) = mass (kg) x gravitational field strength (N/kg) x height (m)
Height usually considered as a change in height
Gpe = mg x triangle h
What’s the equation for kinetic energy
KE = 1/2 x mass x speed squared
Ke = 1/2mv^2
Can we convert gpe to ke
Gpe = ke
Cause of conservation of energy
We can simplify and stuff so v = square root 2g triangle h
Does mass affect the speed of a falling object
No - objects fall to the round at the same rate regardless of their mass but air resistance mean ma they done in practice
How can we investigate finding gravity from energy conservation
We can convert gpe to ke
Measure the velocity that has been reached by a falling object after its fallen under gravity from a known height - then alter the height and measure the velocity and again
If we vary the height from which the object falls, the gpe is different at each bright - which can be converted to ke
If we plot a graph of change in height and v^2 on y axis we will get the gradient of the line to be 2g since v^2 = 2g x change in height
Or take a single measure from the experiment and rearrange experiment to get g - but this is prone to uncertainty from random and systematic errors
How can the reliability of s conclusion be improved
Multiple readings and graphical analysis
Define gravitational potential energy
Is the energy an object has by virtue of its postision in a gravitational field
Define kinetic energy
The energy an object has by virtue of its movement
What is ignored with the conservation of gpe and ke
The effect of air resistance
Is anything ignored in the conservation of energy
No - it insists that no energy can be lost in any scenario
That mad bro
What’s the work done
Th amount of energy transferred- measured in joules
How can force be calculated when energy is transferred mechanically by the means of a force
Work done = force x distance moves in the direction of the force
Triangle W = F x triangle S
Could one confuse triangle W with something
Yes - W for weight
DONT GET CONFUSED
What is the work done on an object gainin gpe
It’s having work done on it against its weight force
W = mg
Work = force x distance = weight x height = mgtriangle h
What direction does friction always act
Always acts in the exact opposite direction to movement
How do we work out work done with a force no acting in the direction of movement
If we want a force and we only know weight
F = mg x cos theta
You can also use sin just make a triangle bro
What is power definition
The rate of energy transfer
Or rate of work done
What’s the formula for power
P =e/t
P= w/t
What is efficiency
The ability of a machine to convert energy usefully
How do we calculate efficiency / define it mathematically
Efficiency = useful work done / total energy input
Effiecny = total energy output / total energy input
Or efficiency = useful power output / total power output
ALWAYS LESS THAN 1
What is the conservation of energy
Requires that energy can never be created or destroyed
