definition of terms and computations

1. THE KINETIC
ENERGY
T H E E N E R G Y O F A M O V I N G O B J E C T

2. THE KINETIC ENERGY
•The word kinetic comes from the greek
word “KINETIKOS” which means
moving.
•Kinetic energy quantifies the amount of
work the object can do because of its
motion.

3. KINETIC ENERGY
 is energy possessed by an object
in motion.
 The earth revolving around the
sun, you walking down the street,
and molecules moving in space all
have kinetic energy.

4. KINETIC ENERGY
Kinetic energy is directly
proportional to the mass of the
object and to the square of its
velocity:
K.E = 1/2 m v2

5. •If the mass has units of kilograms
and the velocity of meters per
second, the kinetic energy has units
of kilograms-meters squared per
second squared. Kinetic energy is
usually measured in units of Joules
(J); one Joule is equal to 1 kg m2 /
s2.

6. CALCULATE THE FOLLOWING USING
THE KINETIC ENERGY FORMULA :
A. A 500 g wooden block moving at 2 m/s.
B. A 71 kg man walking at 1.0 m/s.
C. A 71 kg man running at 5.0 m/s.
D. A 1816 kg car (2 tons) travelling at 26.8 m/s
(60 mph).

7. THE POTENTIAL
ENERGY
T H E E N E R G Y G A I N E D O R L O S T BY T H E O B J E C T

8. THE POTENTIAL ENERGY
• The potential energy is also known as the gravitational potential energy.
• The formula for potential energy depends on the force acting on the
two objects.
• For the gravitational force the formula is P.E. = mgh, where m is the
mass in kilograms, g is the acceleration due to gravity (9.8 m / s2 at the
surface of the earth) and h is the height in meters.
• Notice that gravitational potential energy has the same units as kinetic
energy, kg m2 / s2. In fact, all energy has the same units, kg m2 / s2, and
is measured using the unit Joule (J).
• Examples:
• 1. When you stand at the top of a stairway you have more potential
energy than when you are at the bottom, because the earth can pull you
down through the force of gravity, doing work in the process.
• 2. When you are holding two magnets apart they have more potential

9. FORMULA FOR POTENTIAL ENERGY
W = mgh
NOTE:
Gravity is always constant = 9.8 meter per second
squared. ( 9.8 m/sec² )
Force = weight = mg
W = Fd

10. TRY TO SOLVE THIS :
• A 1.0 kg book is lifted 0.5 m from the table, the force exerted in lifting
the book is equal to its weight.
• Given : 1kg book
• 9.8 m/sec ²
0.5 m
Solution : W = mgh PE = 1kg x 9.8m/sec ² x 0.5m
PE = mgh PE = 4.9 J