Conservation Laws Flashcards

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1
Q

What is energy?

A

The ability to do work. Measured in joules.

Alternatively, it is the ability to apply a force for a given displacement.

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2
Q

What is work?

A

The measure of the amount of energy transferred when a force acts on an object for a given displacement.

The product of the magnitude of applied force and displacement of the object in the direction of the force.

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3
Q

If you push down on a box, and it is moving to the side, how much work have you done?

A

None.

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4
Q

1 Joule. What are the equivalent units?

A

N * m
or
kg * m^2 / s^2

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5
Q

Efficiency equation.

A

(Wout / Win) * 100%

For example, if you put in 100J, but only 50J of work was done, you were 50% efficient.

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6
Q

What is power?

A

The rate at which work is done. Measured in Watts.

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7
Q

1 Watt. Equivalent units.

A

J/s
or
Nm/s
or
kg m^2 / s^3

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8
Q

What is kinetic energy?

A

The energy of motion itself. The energy possessed because of motion.

Ek=1/2 m v^2

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9
Q

What is momentum?

A

How difficult it is to stop an object. A vector quantity with units of kg m/s.

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10
Q

Is momentum conserved in a collision?

A

Yes, always.

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11
Q

How is momentum changed?

A

A net force is needed to change a body’s momentum.

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12
Q

What is an impulse?

A

A force acting on an object for a time. Units are Ns

An impulse is equal to a change in momentum.

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13
Q

What is the difference between elastic and inelastic collisions?

A

In elastic collisions, kinetic energy is conserved. Eki=Ekf
In inelastic collisions, kinetic energy is not conserved.

Note that momentum is always conserved.

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14
Q

What are the different kinds of potential energy?

A

Chemical: gasoline, batteries, etc.
Electric potential: Voltage.
Elastic potential: Springs.
Gravitational potential: Work done by or against gravity.

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15
Q

What is Hooke’s law?

A

Stretch produced by a force applied to a spring was proportional to the magnitude of the force.

F=kx where k is the elastic/spring constant (this changes depending on the spring).

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16
Q

What is mechanical energy?

A

The total of all energy within a system.
Em=Ek+U+Ep
U is the gravitational potential energy.
In an isolated system (no friction/drag), Em is conserved.

17
Q

Gravitational potential energy equation.

A

U=mgh