Unit 4 - Energy (20-28%) Flashcards
What’s a system?
They should be treated like ___.
An object or collection of objects (your definition of what your forces are respective to)
They have no internal structure (e.g. like it’s solid)
The two ways systems can interact:
- A force is exerted by the objects outside the system or between objects within the system
- A transfer/exchange of some quantity with objects outside the system or between objects within the system
Work
The transfer of energy to or from a system through the process of a force being applied over a displacement (a force applied that is external to the system)
Work is based on ___ and ____
the amount of force applied on the object and the displacement of the object
Note: if f and d are in the same direction, work is equal to fd. If not, break f into components (cos(x))
Unit for work:
Joules (J)
If the angle > 90, work is ___.
If the angle < 90, work is ___.
If the angle = 90, work is ___.
Negative
Postive
Zero
Energy
The ability to do work, or the quantitative property that must be transferred to an object in order to perform work on that object
Kinetic Energy is:
Two things that make it larger:
energy to do the motion of an object
greater speed and greater mass
Potential Energy
energy an object has stored with the ability to do work due to its position relative to some “zero” position,
Gravitational Potential Energy is:
Three things that make it larger:
potential energy an object has due to its position within the gravitational field of a massive object, like a planet
mass, height above ground, and gravitational field strength
Elastic Potential Energy is:
Two things that make it larger:
potential energy of an elastic object caused by a force used to deform that object
amount of stretch/compression and the strength of the elastic
Mechanical Energy
The energy an object possesses due to its motion and position. The sum of kinetic energy and the potential energy of a body/system
There’s a direct relationship between work and ____.
What force changes kinetic energy?
kinetic energy (work is positive, KE is positive, and vice versa)
only the component of a force parallel to displacement changes kinetic energy
Equation for work and kinetic energy
work = change in K
(Fdcos(x) = 0.5m(v final)^2 - 0.5m(v initial)^2
If positive work occurs, ME ___.
If negative work occurs, ME ___.
If no work occurs, ME ___.
increases
decreases
doesn’t change
Law of Conservation of Energy
If no work is done on a system by an outside force, then the total mechanical energy of a system remains constant
Overall Takeaways for Physics
- Don’t forget basic math (trig, circle radius, etc.)
- Don’t assume the answer based on logic, must make sense with equation
What doesn’t matter when considering free fall of objects?
What stays the same regardless of the mass of free fall objects (if everything else is the same)?
mass
the velocity
The angle for cosine in the work equation is between the _____ and ____.
force, displacement of the object
An object in a system by itself can only have _____.
kinetic energy
Unit for the spring constant (k):
Newton meters (n/m)
If all energy (like kinetic or potential) are increasing or decreasing, then ____.
mechanical energy is increasing or decreasing
The area of a force vs. displacement graph is the ___.
work
