Energy in motion

3. Contributions of Different
Scientists to the Study of
Energy

19. Conservation of Energy,
Momentum, and Mechanical
Energy

21. In physics, the law of conservation
of energy states that the total
energy of an isolated system
remains constant—it is said to be
conserved over time. Energy can
neither be created nor destroyed;
rather, it transforms from one form
to another.

22. One of the most powerful laws in
physics is the law of momentum
conservation. ... For a collision
occurring between object 1 and
object 2 in an isolated system, the
total momentum of the two
objects before the collision is equal
to the total momentum of the two
objects after the collision.

23. Mechanical energy is the
sum of kinetic and potential
energy in an object that is
used to do work. In other
words, it is energy in an
object due to its motion or
position, or both.

24. Equation 5.1:
EA = EB
Equation 5.2:
KEA + PEA = KEB + PEB

25. Conserving

27. The pictures above illustrate the
concept of momentum. Recall that
momentum ( p ) is a vector quantity
which is equal to the product of the
mass (m) of an object and the change
in its velocity( v ). In symbols:
p = m v

28. Recall Newton’s second law of motion where the
net force Fnet is equal to the product of mass m
and acceleration a.
Fnet = ma
You know that acceleration (a) is the rate of
change of velocity over time ( v/ t) , so:
Fnet = m v/ t
Rearranging the equation, you have:
F t = m v
F t = p

29. Two types of collisions:
Elastic
Inelastic

30. Elastic collisions are collisions in
which both momentum and kinetic
energy are conserved. The total
system kinetic energy before the
collision equals the total system
kinetic energy after the collision. If
total kinetic energy is not conserved,
then the collision is referred to as an
inelastic collision.

31. Inelastic Collision
A collision between bodies in
which part of their kinetic energy is
transformed to another form of
energy, tending to result in the
slowing or joining together of the
bodies.