Work, Energy and Power Flashcards
system
object or group of objects
equation for speed
distance / time
v = s/t
Scalar quantity
quantity described by magnitude only and no direction
Vector quantity
both magnitude and direction must be specified
velocity
speed in a given direction
displacement
straight line of movement
Resultant force
the resultant force is the overall force acting on an object. This is where all the forces can be added together to find one individual force.
If an object is in equilibrium
Then the resultant force is zero
Newtons first law states:
If forces acting on an object are balanced, than the resultant force on the object is zero. If the object is at rest than it will stay stationary.
If the object is moving, then it will stay moving with the same speed and direction.
if an object is balanced:
it will behave as if there is no resultant force acting on it.
why could an object be balanced?
all the forces acting on it would cancel each other out
why do all objects resist a change in velocity
Because all objects need a force to move in the same direction, go faster or slower, or change direction.
equation linking force, mass and acceleration
Force = mass x acceleration
Newtons second law
The second law states that the acceleration of an object is dependent upon two variables - the net force acting upon the object and the mass of the object. The acceleration of an object depends directly upon the net force acting upon the object, and inversely upon the mass of the object. As the force acting upon an object is increased, the acceleration of the object is increased. As the mass of an object is increased, the acceleration of the object is decreased.
Work done
measure of energy transferred
Work done is defined as the amount of force needed to move an object a certain distance. In essence, it is a measure of an energy transferred to or from an object which allows it to be moved.
work done equation
Work done = force x distance
Joule definition
The work done when a 1N force acts through a distance of 1 metre
equation for kinetic energy
Ek=1/2mv2
Kinetic energy = half x mass x velocity squared
Ek in joules
mass in kg
velocity squared in m/s
what happens when a car brakes
work is done by friction between the brakes and the wheel, leading to a transfer of kinetic energy to thermal energy in the brakes.
gravitational potential energy equation
Ep = mgh
gravitational potential energy = mass x gravitational field strength x height
Ep in J
mass in kg
gravitational field strength in N/kg
height in m
power
rate at which energy is transferred or work is done
what happens if the power of a device increases
The more powerful a device is the faster it transfers energy
Equation for power
Power (W) = energy transferred (J) / Time (s)
What would happen if 2 electric motors lift the same weight through the same height.
The one that lifts it faster has more power
What would happen if 2 electric motors lift the same weight through the same height.
The one that lifts it faster has more power
Power efficiency equation
Efficiency = Useful power output / Total power input
Elastic deformation
object returns to original length when extending force removed
Inelastic deformation
object does not return to original length when elastic force removed
Hookes Law
spring extension is directly proportional to force applied.
Hookes law equation
Force = spring constant x extension
F = Ke
force measured in N
spring constant measured in N/m
Extension measured in M
Elastic potential energy equation
Ee=1/2ke^2
Elastic potential energy = 0.5 x spring constant x extension squared
What would happen if a force that streches/compresses a string does work and elastic potential energy is stored in the string?
Provided the string is not inelastically deformed, the work done on the spring and the elastic potential energy stored are equal
