Energy and Conservation Laws
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106 Terms
What is a conservation law?
A law stating that a quantity remains constant in an isolated system.
What happens to the total mass in an isolated system?
It remains constant; mass is conserved.
What is linear momentum?
The mass of an object multiplied by its velocity.
What is the formula for linear momentum?
(p=mv)
Is momentum a scalar or a vector?
A vector because velocity is a vector.
What is the momentum of a stationary object?
Zero.
How does increasing speed affect momentum?
Momentum increases.
How does increasing mass affect momentum at the same velocity?
Momentum increases.
What does Newton’s Second Law state in terms of momentum?
Net external force equals the rate of change of momentum.
What is the formula for force in terms of momentum?
What is required to change an object's momentum?
A net external force.
How does a larger force affect momentum?
Momentum changes more quickly.
What is an isolated system in a collision?
A system with no outside forces changing its total momentum.
What is the law of conservation of linear momentum?
Total linear momentum remains constant in an isolated system.
What happens to total momentum during a collision?
It remains the same before and after the collision.
What is work in physics?
Force multiplied by displacement in the direction of the force.
What is the formula for work when force and displacement are aligned?
(W=Fd)
What is the SI unit of work?
Joule (J).
Is work a scalar or a vector?
A scalar.
When is zero work done?
When there is no displacement or the force is perpendicular to displacement.
Why is no work done when pushing an immovable wall?
The wall does not move, so displacement is zero.
Why does carrying a bag horizontally involve zero work by the upward supporting force?
The force is perpendicular to the horizontal displacement.
Why does centripetal force do zero work in uniform circular motion?
It is perpendicular to the object's motion.
When is positive work done?
When force and displacement are in the same direction.
What does positive work do to a system?
Adds energy to it.
When is negative work done?
When force and displacement are in opposite directions.
What does negative work do to a system?
Removes energy from it.
What is an example of positive work?
Gravity acting on a falling object.
What is an example of negative work?
Friction slowing down a sliding object.
Can work be done during circular motion?
Yes, if the force has a component in the direction of displacement.
What is energy?
The capacity of a system to do work.
What is the SI unit of energy?
Joule (J).
Is energy a scalar or a vector?
A scalar.
What is mechanical energy?
Energy an object has because of its motion, position, or configuration.
What is kinetic energy (KE)?
Energy an object has because it is moving.
What factors affect an object's kinetic energy?
Its mass and speed.
What is the formula for kinetic energy?
What happens to kinetic energy when speed doubles?
It quadruples.
Can kinetic energy be negative?
No, because mass is positive and speed is squared.
Why is kinetic energy relative?
Because speed depends on the observer's reference frame.
Can a rotating object have kinetic energy?
Yes.
What affects the kinetic energy of a spinning object?
Its mass, rotation rate, and mass distribution.
What is potential energy (PE)?
Stored energy due to an object's position or configuration.
What is the formula for gravitational potential energy in your notes?
(PE=mgd)
What do the symbols in (PE=mgd) represent?
(m) = mass, (g) = gravitational acceleration, (d) = vertical displacement.
Why is gravitational potential energy relative?
Height depends on the chosen reference level.
When can gravitational potential energy be negative?
When an object is below the chosen reference level.
What is gravitational potential energy?
Energy associated with position in a gravitational field.
What is elastic potential energy?
Energy stored when an elastic object is stretched, compressed, or twisted.
What must happen to a spring to store elastic potential energy?
Work must be done to stretch or compress it.
- What affects the elastic potential energy stored in a spring?
How much it is stretched or compressed and how strong it is.
- What is internal energy?
The total energy of all atoms and molecules in a substance.
- What happens to internal energy when temperature increases?
Internal energy increases.
- How can friction increase internal energy?
It converts mechanical energy into internal energy, often increasing temperature.
- What happens to gravitational potential energy when a box slides down a ramp with friction?
Some converts into internal energy.
- Can energy converted into internal energy through friction always be recovered as mechanical energy?
No, not all of it can be recovered.
- What happens when work is done on a system?
The system's energy increases.
- What happens when a system does work?
The system's energy decreases.
- What happens when work is done within a system?
One form of energy changes into another.
- What is the law of conservation of energy?
Energy cannot be created or destroyed, only transferred or transformed.
- What happens to total energy in an isolated system?
It remains constant.
- What is an isolated system in terms of energy?
A system that exchanges no energy with its surroundings.
What is the total energy equation for a mechanical system in your notes?
(E=KE+PE)
- What is the relationship between total energy before and after?
Total energy before equals total energy after.
- What happens to a falling object's potential and kinetic energy?
Potential energy decreases as kinetic energy increases.
- During an ideal fall, what happens to total mechanical energy?
It remains constant.
- What is an elastic collision?
A collision in which total kinetic energy is conserved.
- What is conserved in an elastic collision?
Both momentum and kinetic energy.
- What happens when two equal-mass objects collide head-on elastically?
They exchange velocities.
- What happens when a heavy moving object hits a light stationary object elastically?
The heavy object barely slows down.
- What happens when a light moving object hits a heavy stationary object elastically?
The light object rebounds with nearly the same speed.
- What is an inelastic collision?
A collision in which total kinetic energy is not conserved.
- Is momentum conserved in an isolated inelastic collision?
Yes.
- What can happen to kinetic energy in an inelastic collision?
It can transform into heat, sound, or deformation energy.
- What happens to total kinetic energy in an inelastic collision?
It may increase or decrease.
- How do molecular collisions help keep a balloon inflated?
Gas molecules collide with its inner surface and exert pressure.
- How can touching ice lower the temperature of your finger?
Energy transfers from your finger's molecules to the ice's molecules.
- What is a noncontact collision?
An interaction, such as gravitational scattering, that occurs without physical contact.
- What is the slingshot effect or gravity assist?
A spacecraft changes speed or direction by passing near a planet and interacting gravitationally.
- What is power?
The rate at which work is done or energy is transferred.
What is the formula for power?
- What is the SI unit of power?
Watt (W).
- What does one watt equal?
One joule per second.
- How many watts are in one horsepower?
Approximately 746 W.
- What is the difference between work and power?
Work measures energy transferred; power measures how quickly it is transferred.
- Why can a forklift lift bricks faster than a person?
It can produce more power.
- What is the Rule of 70?
An estimate of doubling time based on percentage growth rate.
What is the Rule of 70 formula?
- At 10% annual growth, approximately how long does doubling take?
7 years.
- Can exponential growth continue indefinitely in a real system?
No; limits eventually prevent sustained growth.
- How do scientists define conservation of energy?
Total energy remains constant, although it can be transferred or transformed.
- How is energy conservation commonly understood by the general public in your notes?
Reducing energy use and reliance on nonrenewable sources.
- What is angular momentum?
A measure of rotational motion; for orbital motion, it depends on mass, speed, and radius.
- What is the law of conservation of angular momentum?
Total angular momentum remains constant in an isolated system.
- What is torque?
A twisting effect produced by a force that changes angular momentum.
- What changes angular momentum?
Net external torque.
- Is torque a scalar or a vector?
A vector.
- What is positive torque according to your notes?
Counterclockwise torque.
- What is negative torque according to your notes?
Clockwise torque.
- How is torque related to force?
Net external force changes linear momentum; net external torque changes angular momentum.