Conservation of energy and Collisions Notes
The conservation of energy is a very powerful law. It is easy to
use, mainly because it eliminates time and directions. But
because it eliminates time and directions, it does have its
Conservation of Energy Natural Law Notes
We can now define the concept of energy:
Energy is the capacity to do work (in ideal circumstances).
We all know that we can do work: exert a force through a
distance. But to do that requires food. Thus we convert
Exerting Force and Distance Notes
When you hold something, are you exerting a force on the
When you hold something, are you doing work?
If you set the object on a table, does the table exert a force on
the object? Yes. Does the table do any w
Force and Power Notes
We know how force is related to energy, and how energy is
related to power. Can we relate power to force?
Work = F s , Power = DWork /Dtime =
F Ds /Dt (but Ds/Dt = v), so Power = F v .
Power, like work, is a scalar.
Note that if F is
Contact Force and Energy Notes
Every force we have considered so far has an energy:
gravity (potential energy due to gravity)
friction (energy lost to heat)
spring (potential energy)
What about contact force? Since the contact force is not
normally able t
Escape Speed fractions Notes
In the previous example, we threw something up that went about
32 meters high. How fast would we have to throw something to
make it escape from the earth altogether (if we continue to
neglect air resistance)?
We can use Conser
Forces and Energies Notes
Since Energy is the capacity to do work, and work is force thru a
distance, then we need to consider every force to see what kind
of energy is associated with it.
But from Newtons Second Law, F = ma, is there an energy
Potential Energy for spring Notes
PEspring = -sis Fspring ds where Fspring = -kx
Recall that the minus sign in the PE equation comes from the fact
that to store energy, we need to provide a force opposite that of
the spring. This relation then gives:
Kinetic Energy Notes
If we start with a single net force doing work on an object so that
the object picks up speed (and no other energy is involved), we
Work = sisf F cos(q) ds .
Using Newtons Second Law, with the force simply directed
Gravitational Potential Energy Notes
If we let the force of gravity act on an object as it moves, gravity is
exerting a force through a distance and may add or subtract
energy from the object. We can work with this near the earth
(where gravity is constan