SPS7. Students Will Relate Transformations and Flow of Energy Within a System

Name______Date______Period_____

SPS7. Students will relate transformations and flow of energy within a system.

a. Identify energy transformations within a system (e.g. lighting of a match)

What is Energy?
Energy and Work:
While work is only done when an object experiences a change in its motion, energy can be present in an object or system when nothing is happening at all. Energy is only observed when it is transferred from one object to another.
·  Ex: How can you tell when energy is transferred to an ice cube?
·  Both energy and work are measured in Joules. / Gravitational Potential Energy:
GPE depends on both mass and height.
Assuming each of the apples below have the same mass, which apple has more GPE and why?

Calculating GPE:
Formula: GPE= mgh
·  GPE is measured in Joules.
·  (m) Mass is measured in kg.
·  (g) gravity= 9.8 m/s2
·  (h) Height is measured in meters.
Potential Energy:
Potential energy is stored energy due to position.
Ex: Stretching a rubber band requires work. If you release a stretched rubber band, it will fly out of your hand.
·  Where is energy “stored” in a rubber band?
·  What are some everyday forms of “stored” energy?
Practice Problems:
Calculate the following:
1.  a car with a mass of 1200 kg at the top of a 42 m high hill
2.  a 65 kg climber on top of Mount Everest (8800 m high)
3.  a 0.52 kg bird flying at an altitude of 550 m.
4.  A diver has 3400 J of GPE after stepping onto a diving platform that is 6.0 m above water. What is the diver’s mass in kilograms?
Kinetic Energy
Kinetic energy is energy an object has because of its motion.
Once one of the apples from our example before starts to fall, it has the ability to do work. The potential energy (position) is transformed into kinetic energy (motion).
·  Why does the apple have KE? / Kinetic energy depends on mass and speed.
·  An apple can do more work than a cherry falling at the same speed because an apple has more mass.
·  Two basketballs are rolling down the court at different speeds. Which does more work? Why?
Calculating KE
Formula: KE= ½ mv2
·  KE is measured in Joules
·  (m) Mass is measured in kg.
·  (v) Velocity is measured in m/s.
Kinetic energy depends more on speed than on mass.
Potential Energy vs. Kinetic Energy
The apple has a mass of 20 kg. The tree is 5.1 m high. What is the GPE?
/ Other Forms of Energy:
·  Mechanical Energy
o  The sum of an object’s potential energy and kinetic energy. ME = KE + PE (gasoline engine)
·  Thermal Energy
o  The total potential and kinetic energy of all the microscopic particles in an object. (friction)
·  Chemical Energy
o  Energy stored in chemical bonds. (food, gasoline)
·  Electrical Energy
o  Energy associated with electric charges. (lightning)
·  Electromagnetic Energy
o  A form of energy that travels through space in the form of waves. (sunlight, x-rays)
·  Nuclear Energy
o  The energy stored in atomic nuclei. (sun and stars)
·  Sound Energy
o  Energy that is produced by vibrations of matter and travels through air or other matter as waves. (thunder)
Calculate the following:
1.  What is the kinetic energy of a 44 kg cheetah running at 31 m/s?
2.  Calculate the KE in joules of a 1500 kg car moving at 29 m/s? 18 m/s?
3.  A bowling ball traveling 2.0 m/s has 16 J of KE. What is the mass of the bowling ball in kilograms?