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Energy
Energy
• Is energy involved in the
following things?
– Chewing gum
– Wind blowing
– Water flowing down a
creek
– Sitting still in your desk
– Lighted street lamp
Energy
• Energy
– Every change occurring
requires energy
– Energy is the ability to
cause change
Energy
Different forms or energy:
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Mechanical
Thermal
Radiant
Electrical
Chemical
Nuclear
Sound
Gravitational
Kinetic Energy
• Kinetic Energy
– Energy a moving object
has because of its
motion
– KE = ½ mv²
– Standard unit is the
Joule
Potential Energy
• Potential Energy
– Energy doesn’t have to
involve motion
– Stored energy
– Kinetic vs. Potential
Energy
Elastic Potential Energy
• Elastic Potential Energy
– Energy stored in
something that can
stretch or spring
– Rubber bands or springs
Chemical Potential Energy
• Chemical Potential
Energy
– Energy stored between
chemical bonds
– Food and gasoline
Gravitational Potential Energy
• Gravitational Potential
Energy
– Anything that can fall,
has potential energy
– Energy of an object due
to their position above
the earth’s surface
– GPE = mgh
What exactly is a Joule?
• Joule
– Standard unit of
measurement for energy
– 1 J = 1 kg m²/s²
– 1 J = energy to lift a
small apple 1 meter
straight up
Energy Word Problems
1. What is the kinetic energy of a baseball moving at a speed
of 40 m/s if the baseball as a mass of 0.15 kg?
2. What is the gravitational potential energy of a ceiling
fan that has a mass of 7 kg and is 4 m above the ground?
3. A car is moving at a speed of 20 m/s has a kinetic energy
of 300,000 J. What is the car’s mass?
Conservation of Energy
• Energy is constantly
being transformed from
one form to another
– Light bulbs transform
electrical energy to heat
and light energy
– Gasoline is transformed
into kinetic and heat
energy
• What types of energy
can the sun transform
into?
Conservation of Energy
• Law of Conservation of
Energy
– Energy cannot be
created or destroyed
– Energy is constantly
being changed from one
form to another
Conversion of Energy
• Mechanical energy
– Potential energy + Kinetic energy present in a
mechanical system
– Due to the position and the motion of objects
Work and Energy
• Work
– Transfer of energy that
occurs when a force
makes an object move
– Motion MUST be in the
same direction as the
force
– No movement, NO work
– Force is perpendicular to
motion, NO work
No Work is Being Done!!
• No movement
• Force perpendicular
to motion
Work is Being Done!
• Work is being done IF:
– Object moves
– Motion is in the same
direction as the force
Calculating Work
• Calculating work
– W = force x distance
– Standard unit = Newton
meter OR Joule
– Energy, Work and Power
• How much work is the
girl doing on the bicycle?
Power
• Power
– Amount of work done in
one second
– Rate at which work is
done
– P = Work ÷ Time
– Unit is the Watt
– Power – Watts
– 1 horsepower = 746
watts
Machines
• Machines
– Device that makes doing
work easier
1. Increases force
2. Changes direction of
the force
Machines
• Input force
– Force applied to the
machine
• Output force
– Force applied by the
machine
• Mechanical Advantage
– Ratio of the output force
to the input force
– MA = Output force ÷
Input force
Machines
• Efficiency
– Measure of the amount
of work put into the
machine is changed to
useful output
– Efficiency =
• (Output ÷ input) X 100%
Simple Machines
• Levers
– Bar that is free to pivot
about a fixed point
– 1st Class
– 2nd Class
– 3rd Class
Examples of Levers
• Examples of Levers
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Screwdriver
Wheelbarrow
Baseball bat
Our elbow
Seesaw
Scissors
Simple Machines
• Pulleys
– Grooved wheel with a
rope, chain or cable
running along the groove
– Examples of machines
that use pulleys
• Flag poles
• Sail boats
• Weight machines
Simple Machines
• Wheel and Axle
– Shaft or axle attached to
the center of a wheel
– Examples:
• Wheel and axle of a car
• Wheel and axle of a
bicycle
• Handle of a pencil
sharpener
Examples of Wheel and Axles
Simple Machine
• Incline Plane
– Sloping surface
– Examples include:
• Stairs
• Ramps
Simple Machine
• Screw
– Incline plane wrapped
around a cylindrical post
– Examples:
• Jar lid
• Wood screw
• Light bulb
Simple Machine
• Wedge
– Inclined plane with one
or two sloping sides
– Examples:
• Knife
• Scissors blade
• Ax
Identify the following simple machines
Identify the following simple machines
Identify the following simple machines
• Compound Machines
– Two or more simple
machines combined