Physics Work and Energy
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Transcript of Physics Work and Energy
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Section 1 Work
Section 2 Energy
Section 3 Conservation of Energy
Section 4 Power
Mr. Thompson's Physics Class
What do you think? List five examples of things you have done in the last year that
you would consider work. Based on these examples, how do you define work?
Mr. Thompson's Physics Class
Work In physics, work is the magnitude of the force (F) times the
magnitude of the displacement (d) in the same direction as the force.
W = Fd What are the SI units for work?
Force units (N) x distance units (m) N•m are also called joules (J).
How much work is 1 joule? Lift an apple weighing about 1 N from the floor to the
desk, a distance of about 1 m.
Mr. Thompson's Physics Class
Work In physics, work is the magnitude of the force (F) times the
magnitude of the displacement (d) in the same direction as the force.
W = Fd What are the SI units for work?
Force units (N) x distance units (m) N•m are also called joules (J).
How much work is 1 joule? Lift an apple weighing about 1 N from the floor to the
desk, a distance of about 1 m.
Mr. Thompson's Physics Class
Work and Energy Section 1
© Houghton Mifflin Harcourt Publishing Company
Work
• Pushing this car is work because F and d are in the same direction.
• Why aren’t the following tasks considered work?– A student holds a heavy chair at arm’s
length for several minutes.– A student carries a bucket of water along
a horizontal path while walking at a constant velocity.
Mr. Thompson's Physics Class
Work and Energy Section 1
© Houghton Mifflin Harcourt Publishing Company
WorkHow would you calculate the work in this case?What is the component of F in the direction of d?
• F cos
– If the angle is 90°, what is the component of F in the direction of d?
• F cos 90° = 0– If the angle is 0°, what is the
component of F in the direction of d?• F cos 0° = F
Mr. Thompson's Physics Class
Work
Mr. Thompson's Physics Class
Work is a Scalar Work can be
positive or negative but does not have a direction.
What is the angle between F and d in each case?
Mr. Thompson's Physics Class
Classroom Practice Problem A 20.0 kg suitcase is raised 3.0 m above a
platform. How much work is done on the suitcase?
Answer: 5.9 x 102 J or 590 J
Mr. Thompson's Physics Class
Now what do you think? Based on the physics definition, list
five examples of things you have done in the last year that you would consider work.
Mr. Thompson's Physics Class