Potential Energy and Conservation of energy Flashcards
Potential energy EP
Energy associated with the configuration of a system of objects that exert forces on one another.
Conservative force
Force
The net work done by a conservative force on a particle moving around any closed path is zero!
With a conservative force, any choice of path between the points gives the same amount of work.
Non conservative force
A force that is not conservative
Gravitational potential energy
Potential energy that correspond to gravitational force.
ΔEP = mgΔy | EP(y) = mgy
Δy = Δh -> vertical position!
Potential energy associated with a particle–Earth system.
Elastic potential energy
Potential energy associated with a particle–spring system.
EP(x) = 1/2 k x^2
x->position of the block
Mechanical energy of the system
Sum of Kinetic and Potential energies.
EM = K + EP
Conservation of mechanical energy
K1 + EP1 = K1 + EP2
sum of K and EP for any state of the system = sum of K and EP for any other state of the system.
In an isolated system where only conservative forces cause energy changes EM cannot change!
ΔEM = ΔK + ΔEP = 0
Law of conservation of energy
The total energy E of a system can change only by amounts of energy that are transferred to or from the system
W = ΔE = ΔEM + ΔEth + Eint
Eth
Work of conservative forces in isolated system
When the conservative force does work W on a particle within the system, the change ΔEP in the potential energy of the system is ΔEP = - W
When we have the function of F(x) and object moves from xi to xf then we can calculate the ΔEP as the “minus” integral of F(x) from xi to xf
Potential energy curves
If we know the curve U(x) of the Potential energy we can find F(x) as -dU(x)/dx
The particle is in equilibrium at points where the slope of the U(x) curve is zero -> F(x)=0
Turning point
A point x at which the particle reverses its motion, K=0
Work done on a system by an external force
Work W is energy transferred to or from a system by means of an external force acting on the system.
When there is no friction : W = ΔEM
When there is friction: W = ΔEM + ΔEth
Power
The power due to a force is the rate at which that force
transfers energy.
P= ΔE/Δt
