Section 4.1 - The Nature of Energy. Warm-Up: Examine your lab data from yesterday. What relationship...
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Transcript of Section 4.1 - The Nature of Energy. Warm-Up: Examine your lab data from yesterday. What relationship...
Section 4.1 - The Nature of Energy
WEDNESDAY, 11/27• Warm-Up:
• Examine your lab data from yesterday. What relationship do you notice between momentum and kinetic energy? Can you think about why this might be true?
• Learning Goal(s): Compare and contrast kinetic energy and momentum.
• Agenda: - 1. Warm-Up2. Work on Analysis and Conclusions for the Kinetic Energy
Lab3. Complete the Kinetic Energy and Potential Energy Problem
Set
•HW: Kinetic Energy and Potential Energy Problem Set (1st side only) due on Tuesday, 12/3
Have a Happy Thanksgiving!
Kinetic Energy vs. Momentum
0 1 2 3 4 5 6 7 80
100
200
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400
500
600
700
MomentumKinetic Energy
Students
Mom
entu
m (k
gxm
/s)
Kine
tic E
nerg
y (J)
What Is Energy?
• Changes are constantly occurring in the world.– Examples: light bulbs heating the air, sunlight on
window, you breathing
• Every change requires energy.
• Energy – ability to cause change
Energy is Found in Many Forms• Electromagnetic energy – energy in waves
– Examples: UV, Infrared, Radio • Mechanical – energy in physical movement
– Examples: moving car, flying baseball• Electrical energy – energy carried by moving electrons• Heat – thermal energy
– Example: cup of hot tea• Chemical – stored in molecules
– Example: food, batteries• Nuclear – energy stored in the nucleus of an atom
– Example: Uranium used in nuclear reactors• Kinetic – energy an object in motion has
– Example: person running, roller coaster going down a hill• Potential – stored energy due to an object’s position
– Example: roller coaster at the top of a hill
Units of Energy – the Joule
• Units of energy• kg x m2/s2
• Abbreviated J
James Prescott Joule
Kinetic Energy
• Energy a moving object has because of its motion.
• Depends on an object’s mass and its speed.
KE = ½ mv2
KE – kinetic energy in Joules (J)m – mass in kg
v – velocity (m/s)
Examples of Solving for Kinetic Energy
• A jogger with a mass of 60 kg is moving at a speed of 3 m/s. What is the kinetic energy?
• A bowling ball is moving with 300 J of energy. The ball weighs 2 kg. How fast is the ball moving?
Potential Energy
• Stored energy due to an object’s position
Three types:– Elastic potential energy – energy stored by something that
can stretch or compress
– Chemical potential energy – energy stored in chemical bonds
– Gravitational potential energy – energy stored in objects due to their position above the Earth’s surface
Solving for Potential Energy
GPE = mgh
GPE – gravitational potential energy (in J)m – mass (in kg)
g – 9.8 m/s2
h – height (in m)
Examples of Solving for Potential Energy
• What is the gravitational potential energy of a ceiling fan that has a mass of 7 kg and is 4 m above the ground?
• How high above the ground is a baseball with a mass of 0.15 kg and a GPE of 73.5 J?
Changing GPE
• As an object begins to fall it has GPE and KE.• As the object gets closer to the ground it has
less GPE and more KE.
• Example – An 80 kg skydiver jumps from a 10 m platform. What is the GPE of the skydiver at the top of the platform? What is the GPE of skydiver after falling 5 m?
Changing GPE – Energy Diagram