Chapter-6 Energy and Oscillations

1
Chapter-6 Energy and Oscillations
2
Outline

• 1 Simple Machines, Work, and Power
• 2 Kinetic Energy
• 3 Potential Energy
• 4 Conservation of Energy
• 5 Springs and Simple Harmonic Motion
• Everyday Phenomenon Energy and the Pole Vault

3
Motion of a Pendulum
4
Motion of a Pendulum

• Pendulum motion intrigued Galileo.
• Things to consider
• Velocity
• Acceleration
• Energy

5
Simple Machines

• A simple machine is any mechanical device that
  multiplies the effect of an applied force.

Ex Lever
6
Mechanical Advantage is the ratio of the output
force to the input force.
7
Work
8
Work
Work may mean different things in everyday life.
In physics, we define the work done on an object
by a force as, Work Force ? Distance. W F ?
d. Here the force acts along the distance.
9
Units
1CGS- centimeter, gram, second. 2SI-
International System. 3BE- British
Engineering. 4USC- Unites States Customary.
10
Does any force do work?

1. Push on a wall
2. Carry a weight and walk horizontally

11
Does any force do work?
12
E2
13
Power
The rate at which work is done is called the
power.
14
Power
The rate at which work is done is called the
power.
15
Power
The rate at which work is done is called the
power.
Power is a scalar quantity. The SI unit for power
is Watt, W. 1 W 1 J/s. Before the arrival of
machines horses were used to do work. With this
originated the unit horsepower, hp. 1 hp 746 W
550 ft/lb/s.
16
Problem

• A person weighs 110 lbs, climbs 10 steps of
  stairs, in 5 second. If the height of a step is 6
  inches. Calculate the work and power.

17
6.2 Kinetic Energy
Kinetic energy is the energy of motion. The word
kinetic originated from the Greek word
kinetikos, meaning motion.
18
6.2 Kinetic Energy
Kinetic energy is the energy of motion. The word
kinetic originated from the Greek word
kinetikos, meaning motion. If an object of
mass, m moves with a velocity v, then the kinetic
energy, KE is given by the following equation,
19
6.2 Kinetic Energy
Kinetic energy is the energy of motion. The word
kinetic originated from the Greek word
kinetikos, meaning motion. If an object of
mass, m moves with a velocity v, then the kinetic
energy, KE is given by the following equation,
Kinetic energy is a scalar quantity. It also has
the same unit as work, joule (J). 1 J 1
kg.m2/s2.
20
W F ? d KEf ? KEi.
21
What is negative work?
22
6.3 Gravitational Potential Energy
23
Gravitational Potential Energy
Gravitational potential energy, GPE is the energy
stored in an object as a result of its height. It
can be calculated using weight, which is mass
times gravity, and height. It is given by the
following equation,
Gravitational potential energy is a scalar
quantity. The SI unit for it is also joule, J.
24
The gravitational potential energy of raised
crate can be converted to kinetic energy
25
Elastic Potential Energy, EPE
26
Elastic Potential Energy, EPE
27
Elastic Potential Energy, EPE
28
Conservative Forces
A force is conservative if the work it does on
moving an object is independent of the path.
Gravitational force is a conservative force. The
work required against gravity to move an object
between two points depends on the height between
the objects. It does not depend on the path taken
to move the object between the two points. Other
conservative forces are elastic spring force,
magnetic force, and electric force.
29
6.4 Conservation of Energy
30
Work done on a pendulum
31
Conservation of Mechanical Energy

• Mechanical energy KE PE
• In the presence only conservative forces, the
  total mechanical energy of a system remains a
  constant.

32
Try this box 6.4
33
How is energy analysis like accounting?
34
Pole Vault
35
6.5 Springs and Simple Harmonic Motion
36
Simple Harmonic Motion
37
Simple Harmonic Motion
Amplitude is the maximum distance from
equilibrium. Period, T is the time taken for one
complete cycle. Frequency Number of cycles per
unit time.