Page 100 -
P. 100
10.3 Kinetic and potential energy
A crane or excavator Kinetic energy
with a massive steel When you observe the world around you, you see many moving
ball on a chain is objects, such as vehicles and people. When a physical body or substance
used for demolishing is moving, it stores kinetic energy. This is an energy transfer that is
textbooks nis edu kz
some buildings. How linked with movement. When a force is applied, you can speed up a
physical body (or substance) or slow it down – and so its kinetic energy
does the ball manage
changes. In other words, a force acting on the object must do work (i.e.
to break through
transfer energy) in order to change the kinetic energy.
solid walls?
REMEMBER! The kinetic energy of an object is defined by the
following equation:
2
v where = mass of object (kg)
E K
2 v = speed of the object (m/s)
E K = kinetic energy (J)
Gravitational potential energy
OVER TO YOU! As the ball moves
upward, it slows down
Look at the image below. and stops for an instant
What are the energy transfers
When you throw a ball upwards As the ball moves downwards it
happening in the player? it is moving the fastest so it has speeds up and the potential energy
What are the energy transfers maximum kinetic energy is transferred into kinetic energy
happening to the ball?
Describe these transfers. From our everyday experience we know that when we throw an object
upward, it falls back down after reaching certain height. To understand this
phenomenon we use the concept of energy transfers.
As you throw an object upward, your hand transfers its kinetic energy to
the object. As the object leaves your hand, it does so at its maximum speed
and therefore at its maximum kinetic energy. The moment the object
leaves your hand, forces exerted by gravity and air resistance begin to slow
it down. As it continues to travel upwards, it transfers its kinetic energy to
gravitational potential energy. Then once it reaches its maximum height, it
falls back down and speeds up again, transferring its potential energy back
into kinetic energy (i.e. gaining kinetic energy once more).
REMEMBER! The potential energy of an object is defined by the
following equation: E p = mgh
where m = mass of object (kg)
2
g = gravitational acceleration (m/s )
h = height (m)
E = potential energy (J)
100 p
