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3. Motion
– ENERGY
All life depends upon energy which allows us to move and interact with our environment.
Formally energy is defined as the ability or capacity to do work. Most of the energy on the earth
comes from the sun.
All energy originates from four fundamental forces: strong nuclear forces, weak nuclear forces,
gravitational forces, and electromagnetic forces. We find that these fundamental forces act to produce
common forms of energy in our environment. These forms include: thermal, light, sound,
mechanical, electrical, chemical, and nuclear.
The various forms of energy can be indicated by two types, potential and kinetic energy. They
are described by the amount of stored (potential) and/or dynamic (kinetic) energy they possess.
Potential Energy is the energy stored by an object as a result of its position or the position of
its parts. A rock on a table, a bowl of cereal, a stick of dynamite, and a tank of gasoline are all
examples of objects that have energy stored in atoms or molecules. The rock has potential energy
because of its height that can be released and converted to kinetic energy and heat, if it is dropped.
Potential energy is equal to force (newtons) multiplied by distance. (meters).The units of
measurement is newton-meters and is referred to as a joule (1 newton-meter = 1 joule).
Remembering that f=m x a where f = force, m= mass and d= distance. In this investigation the d will
be the height (h) which the truck drops and a is due to gravity (g) then f=m x g. This relationship is
often written P.E. = mgh
Potential Energy = mass x acceleration of gravity x height
Where:
m =
g =
h =
or
P.E. = m x g x h
the mass of the object measured in kilograms.
the acceleration of gravity, on planet Earth, 9.8 meters / second2.
height in meters that the object falls measured in meters.
For Example: When m = 378 Kg, g= 9.8 m/sec2 and h = 200 m
P.E. = mgh
P.E. = 378 kg x 9.8 m/sec2 x 200 m
Note: 1 kilogram- meter / sec2 is 1 newton which is 1 joule.
P.E. = 740,880 N-m or 740,880 joules
Kinetic Energy is the dynamic energy that matter has because of its motion and mass.
Examples of kinetic energy are: moving car, a falling rock, a bullet shot from a gun or a flow of
electrons. The unit of measurement is labeled newton-meters. 1 newton-meter is 1 joule.
Kinetic Energy = 1/2 mass x velocity2 or
Where:
m =
v =
K.E. = 1/2 m x v2
the mass of the object moved is measured in Kilograms.
the velocity measured in meters per second.
For Example: When m = 1000 kg and v 38.5 m/s
K.E. = 1/2 x m x v2
K.E. = 1/2 x 1000 kg x (38.5m/s x 38.5m/s)
K.E. = 1/2 x 1482300 kg-m2/s2
K.E. = 741,125 kg-m2/s2 = 741,125 newton-meter = 741,125 joules
Energy
Track Thickness = 0.0075-m
0.3800-m
0.4000 -m
1. Does Energy Depend On Height (Force)?
a. In this experiment we will keep the timed distance, mass of the truck, support block
position and starting position constant while varying the height of the support block which
will change the force on the truck.
b. Obtain the force exerted by the truck due to the height by watching the video laboratory.
c. Obtain the times for the three trials for each height by watching the video laboratory.
d. Calculate the average time, velocity, potential and kinetic energy. Formulas are provided.
Time Trials
Block
Height
(meters)
Height of
Truck (h)
(meters)
Force on
Truck
(Newton)
Trial
1
Trial
2
Trial
3
(seconds)
(seconds)
(seconds)
Speed
Average
Time
(seconds)
V=d/t
(m / sec)
Energy
Potential
P.E.= mgh
K.E.= ½ mv2
Kinetic
(Joules)
(Joules)
0.0300
0.0600
0.0900
e.
f.
g.
h.
Does the change in height (force) on the truck effect time and energy, explain?
Explain why potential energy and kinetic energy are not numerically equal.
Does the change in height (force) on the truck effect time and energy, explain? _____
Explain why P.E. and K.E. are not equal. _____
2. Does Energy Depend On Mass?
a. In this experiment we will keep the timed distance, support block height, support block
position and starting position constant while varying the mass of the truck.
b. Obtain the force exerted by the truck due to the mass by watching the video laboratory.
c. Obtain the times for the three trials for each mass by watching the video laboratory.
d. Calculate the average time, velocity, potential and kinetic energy. Formulas are provided.
Time Trials
Mass of
Truck
(Kg)
Force on
Truck
(newton)
Height of
Truck (h)
(meters)
0.0600
0.0375
0.1200
0.0375
0.1800
0.0375
0.2400
0.0375
Trial
Speed
Trial
Trial
1
2
3
Average
Time
(sec.)
(sec.)
(sec.)
(seconds)
V=d/t
(m / sec)
Energy
Potential
P.E.= mgh
(joules)
Kinetic
K.E.= ½ mv2
(joules)
e. Does the change in mass affect time and energy?
f. Explain why potential energy and kinetic energy are not the same.
g. How does the change in mass affect velocity and energy?
h. Explain why P.E. and K.E. are not equal.
3. Efficiency
Since potential energy is the total theoretical energy and the kinetic was the actual energy one
could determine the efficiency. Do this for truck without added mass.
% efficiency =
(potential energy − kinetic energy)
potential energy
* 100