lab 6 Flashcards
In a pendulum system, the potential energy can be calculated using
the angle and length of the pendulum:
h = L (1 – cos θ)
Conservation of Energy
The law of conservation of energy states that
energy cannot be created or destroyed – it can only be transformed. Conservation of Energy applies to the sum of all energies in a system, but in this experiment we consider only two forms of mechanical energy:
Total Mechanical Energy=KE+PE (perfect case-frictionless)(energy is conserved)
In this experiment, we will observe how this occurs in a system without nonconservative forces
In this experiment, we will observe how this occurs in a system without nonconservative forces (forces that can dissipate mechanical energy) as well as in a system that includes friction, which is a nonconservative force. Although the system with friction will not conserve total mechanical energy, it will be shown that total energy is still conserved in this case. In this case, we can expand our calculation of total energy to include the energy dissipated as heat as a result of friction:
Total Energy=KE+PE+(Thermal Energy)
(friction force acting on it, energy is not conserved) (Eq. 4)
How does changing the angle affect the energy in the system and the motion overall?
Changing the angle affects the height of the mass which will change the momentum and then this affects the total energy seen in the table. There are different total energies for the different angles.
Evaluate your results and discuss the difference between the system without friction and with friction included.
The energy turns into thermal energy because of friction since it makes the pendulum loose its momentum as we have calculated in table two. The initial and final total mechanical energy are different, the final total mechanical energy decreases, and it turns into thermal energy instead.
Does Friction violate Conservation of Energy?
It doesn’t violate the conservation of energy since the energy that is lost is then given off as thermal energy because of friction.
The length of a pendulum is 25 cm, and the mass of the bob is 300 g. It is displaced from the equilibrium position and released. At the lowest point of the trajectory the KE of the pendulum is 0.265 J.
A. How fast is the pendulum moving when at the lowest point?
KE= ½ (m) (v)^2
0.265= ½ (.3kg)(v)^2
V=1.33
B. From what height (above the lowest point of the trajectory) was it released?
TE= 0.265
PE= mgh
0.265=(.3kg)(9.81)h
H=9.01 *10^-2
D. The pendulum is passing through a point 5 cm above its equilibrium position (its lowest point).
- find its PE
- find its PE
PE=mgh
PE= (.3kg)(9.81)(0.05)
PE=0.15 - find its KE
KE= ½ (m) (v)^2
KE=0.265-0.15
KE=0.115
conservation of energy
always constant, no change before and after when there is no external force acting on it
Momentum is conserved
is the momentum of moon conserved
yes it is conserved unless acted on external force
best example for conservation of energy
pendelum
TE stays the same just
an energy transfer from PE to KE
TE stays constant in a frictionless state
