10. Energy Flashcards
What is Energy?
Energy is the ability to do work
Scalar quantity
What are the two main types of Energy?
Kinetic Energy (KE)
Potential Energy (PE)
What is Kinetic Energy?
KE is the ability to due work when moving or
The ability to apply a force so there is a displacement because of movement - (Translational or rotational)
- KE = ½mv2
- Units: Joules (J)
A moving bowling ball will knock down the stationary pins.
How can work be increased in this situation?
The faster the ball is thrown the more work you can do
The heavier the ball used, the more work you can do
What is Potential Energy?
PE is the ability to due work because of position or
The ability to apply a force to create movement is dependent upon the position of an object
- PE = mgh
- Units: Joules (J)
A hammer dropped onto a nail will push the nail into the wood. How can work be increased in this situation?
The higher the hammer is held from the nail, the more work you can do
The heavier the hammer you use, the more work you can do
To do work requires a change in energy
How are Work, KE and PE related?
A force must be applied in order to stop the ball. How much work is required to catch a 1.4 kg baseball that is traveling at 42 m/s?
W=∆KE
W= (0.5mv^2)f - (0.5mv^2)i
W= 0-(0.5)(1.4)(42^2)
W=-1234.8 J
Athletes apply force upon landing -> creating a reaction force. The reaction force stops the athlete from moving
How can displacement be used to decrease the reaction force?
As displacement increases, the impact forces decrease, so the reaction force decreases.
Thus landing on deformable objects dcreases impact forces
What is the Work-Energy Theorum?
Energy CANNOT be created or destroyed
- Energy can be transferred from one system to another
- Energy can be transformed from one type to another
As a ball is dropped from a height, it loses potential energy
As the ball drops, the faster it travels gaining kinetic energy
This assumes that no deformation occurs to the systems
When gravity is the only acting external force, how does Mechanical Energy change?
When gravity is the only acting external force,
a body’s mechanical energy (C) remains constant
How do KE and PE behave in this case?
Imagine a 60 kg man jumps upwards with an initial vertical velocity of 2.5 m/s. The maximum vertical displacement would be 0.32 m. What would ME be at takeoff and maximum height?
Why is running on loose sand more fatiguing than running on a rubberized track?
When running on sand, there is less reaction force pushing back and propelling you forward becasue the ground is not rigid, so it absorbs some of the force.
How do Work, Power and Energy differ?
Work
- Applying forces to a system to move the object
Transferring energy from one system to another
Power
- The rate at which work is performed
Energy
- The ability to do work
- Because the system is in motion
- Because the system has the potential to move due to height
