Unit 3 Flashcards
impulse is equal to…
…change in momentum
What do you need in order to cause a change in momentum?
Have to exert an impulse.
Impulse equation
impulse = force * time interval = Ft Ft = change in momentum = (change in m*v)
Momentum equation
Momentum = mass * velocity = mv OR mass * speed
Momentum
Inertia in motion
A moving object can have a large momentum if it…
…has a large mass, a high speed, or both.
What produces acceleration?
Force.
Impulse
Change in momentum depends on the force that acts the length of time it acts.
Decrease momentum
Extend the time of contact, reduce the force of the catch.
The impulse required to bring an object to a stop and then to “throw it back again” is…
…greater than the impulse required merely to bring the object to a stop.
Law of Conservation of Momentum
States that, in the absence of an external force, the momentum of a system remains unchanged.
Whenever objects collide in the absence of external forces…
…the net momentum of both objects before the collision equals the net momentum of both objects after the collision.
Elastic collision
When objects collide without being permanently deformed and without generating heat.
Inelastic collision
A collision in which the colliding objects become distorted and generate heat during the collision.
Equation conservation of momentum
net momentum(before collision) = net momentum(after collision)
OR
(net mv)before = (net mv)after
Vector sum of momenta is…
…the same before and after a collision
The force or impulse must be exerted on the object by something….
…outside the object.
Momentum is conserved only when interacting objects move along…
…the same straight path
With the absence of air resistance in space…
gravity is the only opposing force that affects two docking space stations.
Properties of energy
- is conserved
- cannot be created or destroyed
- can change form
- measured in joules
Work
Product of a net force on an object and the distance through which the object is moved.
Power
Rate at which work is done.
Power equation
(work done)/(time interval)
Measured in watts.
Mechanical energy
Energy due to the position or the movement of something. Kinetic and potential energy
Potential energy
(PE). In stored state it has the potential for doing work. Three examples: elastic potential, chemical, and gravitational potential.
Kinetic energy
energy of motion. Not moving: zero units of energy.
Energy
Property of an object on system that enables it to do work. Measured in joules
Work is done when…
a force acts on an object that results in the object moving in direction of the force.
Work equation
work = net force * distance W = Fd
1 joule =
1N/1m
Gravitational potential energy
gravitational potential energy = weight * height
PE = mg * h
Kinetic energy equation
kinetic energy = (1/2)mass * speed^2
KE = (1/2)mv^2
net force * distance = KE
Fd = (1/2)mv^2
Work-energy theorem
work = (change in)KE. Whenever work is done, energy changes
Law of conservation of energy
States that energy cannot be created or destroyed. It can be transformed from one form into another, but the total amount of energy never changes.
Machine
Device used to multiply forces or simply change the direction of forces.
Machine function
Transfers energy from one place to another or transforms it from one form to another.
Lever
Machine made of a bar that turns about a fixed point.
work input = work output
(force*distance)input = (force * distance)output
Mechanical advantage
(ratio output force)/(ratio input force)
Pulley
Kind of lever that can be used to maintain the direction of force or change the direction of a force. can also multiply the force involved, but the amount of work done stays the same.
In any machine…
…some energy is transformed into atomic or molecular kinetic energy - making the machine warmer.
Efficiency of a machine
efficiency = (useful work output)/(total work input)
Efficiency percentage
(actual mechanical advantage)/(theoretical mechanical advantage)
Energy for life
there is more energy stored in the molecules in food than there is in the reaction products after food is metabolized. This energy difference sustains life.
Fuel Cell
When one makes electrolysis process run backwards.
1MW =
1,000,000W
1 unit horsepower =
0.75kW
What happens when simple lever rocks about its fulcrum, or a pulley turns about its axis?
A small fraction of input energy is converted into thermal energy.
two ways to calculate gravitational potential energy?
Weight times height or mass times acceleration due to gravity (g) times height are the two ways to calculate gravitational potential energy.
Why can wind be considered a type of solar power?
Wind is caused by unequal warming of Earth’s surface.
If momentum is changing but mass remains the same, then…
…velocity must be changing.
If velocity is changing then…
…the object is accelerating.
Acceleration always means that…
…there is a net force.
