potential energy. potential energy examples give four examples of an object that has potential...
TRANSCRIPT
Potential Energy
Potential Energy examples
• Give four examples of an object that has potential energy (not mentioned in the previous power point)
Potential energy – the energy an object or system has by virtue of its position or
configuration
Gravitational Potential Energy (UG)
• Energy stored due to an object’s position or vertical height
Recall…
• We defined energy as an object’s ability to do work and….
• Work = Force x DisplacementIn order to gain potential energy due to gravity, somebody/something must put the “work” into the system• Knowing this, we can transform the Work
equation into one for gravitational potential energy
UG Equation
– Work = Force x Displacement• The force that must be overcome is due to gravity,
therefore, Force = mass x gravity.• When changing an object’s vertical position, you cause
a displacement…and we’ll just call that h, for height
– Now….• Work = (mass x gravity) x height
– Once the work has been put into the system, it turns into energy…therefore
– UG= mgh
Calculating UG
• Calculate the UG contained by an Will I. Flye (80 kg), jumping from a height of 1800 meters.
• Will’s friend, May B. Knot, has a smaller mass (65 kg), but jumps from 1900 meters. Who has more UG?
Energy Transfer
Will and May land…how much UG do they contain now?• Knowing energy cannot be created or
destroyed, where did the energy go?
Energy Transfer
• The answer lies in energy’s ability to transform into other forms.
• Will I. Flye and May B. Knot had UG to begin with, but were not moving.
• After jumping off the cliff, explain what happens?• They start accelerating towards the ground• Their height decreases• They transferred UG into kinetic energy, K (moving
energy)
Other examples of UG transfers into K
• Write down an example of another transfer similar to this one
Recalling an earlier picture…
• Why does Katniss have potential energy?
• Is this UG?
• This is called elastic potential energy, Us
Elastic Potential Energy, Us
• Scalar• Measured in Joules, J • the energy stored in
elastic materials as the result of their stretching or compressing
Meet Mudd…
• http://www.youtube.com/watch?v=tU9RSNXaElw
Calculations using Us
• Us=1/2kx2
• k = spring constant– Measures how “stiff” the
spring is. – Higher the k, the stiffer
the spring– Units are N/m
• x = displacement from equilibrium position
• Mudd, the jumping bulldog, has a mass of 25 kg, the trampoline has spring constant of 25,000 N/m, and he compresses it 0.1 meters.
• How much Us does the trampoline contain?
Other examples of energy transfers…
• http://youtu.be/ALdXhl7zveY?t=50s• http://youtu.be/F92FQdnLlSc?t=39s