Forms of Energy
What is energy?
The ability to perform work
What's the difference between a physical law and other laws?
Physical laws cannot be broken, while regular laws can be broken by people who do not wish to follow the rules.
God designed the world with physical laws that are always followed! We cannot choose to not transfer our momentum to objects we collide with.
What is a force?
A push or a pull
What is the scientific definition of work
A change in position due to an applied force.
What is power?
Work done over time, or the rate at which work is done.
As a plane takes off, what happens to its gravitational potential energy?
Gravitational potential energy increases as the plane's height increases.
P.E. = mgh
First Law of Thermodynamics
In a closed system, energy can neither be created nor transformed. It can only be transferred or transformed.
If a fast, heavy object hits a still, light object, what happens?
The object with more mass and speed has more momentum, so it will transfer momentum to the object at rest and cause it to move.
Force is directly related to what physical property?
Mass! The greater the mass, the greater the force needed in order to move the object
What are the factors that determine power?
Work, and time.
More work in less time = greater power
The same work in more time = less power
What factors influence kinetic energy?
K.E. = 1/2mv2
m = mass
v = velocity
Describe the Law of Conservation of Momentum
Changes of momentum in a closed system must be equal.
Why do boats float?
Buoyancy: Boats displace enough water to cause enough force to keep it from sinking.
Recall our hiker that zig zags up the mountain, and our climber that climbs straight to the top. Which performs more work?
They perform the same work, they traveled the same vertical distance.
How do machines use power to improve our lives?
They perform more work in a shorter amount of time, enabling us to be more efficient!
The term used to describe the scientific study of motion?
Mechanics
Give two examples other than energy of things that are "conserved".
Momentum, Mass
Define friction.
A force that opposes motion.
True or False:
Work can be performed even if nothing is moved, as long as a large force is being applied.
False
Work requires that the object is actually moved!
Imagine a person walking for 20 minutes, and a car driving for 20 minutes. Which will get further, and why?
The car performs will get further, because it has more power than the person so it will be able to perform more work in the same amount of time.
Give an example of an object with potential and kinetic energy, and describe when it has more potential energy than kinetic.
Example: A pendulum, at the top of the swing it has all potential energy, but while it is swinging it has a combination of kinetic and potential energy.
What is the law of conservation of mass?
Matter cannot be created nor destroyed.
If a boat is traveling west at 15 m/s, but the current is moving east at 10 m/s, which direction is the boat going and what is its velocity?
The boat is going west at 5 m/s.
15 m/s west - 10 m/s east = 5 m/s west
Describe the work being done when a person rolls down a hill on a bike without peddling.
Gravity is applying the force in order to do the work to move the bike down the hill.
Recall our hiker that zig zags up the mountain, and our climber that climbs straight to the top. It took the climber 2 hours to reach the top, but the hiker 4 hours.
Which used more power?
The climber = he traveled the same distance, performed the same amount of work as the hiker, but in less time.