Physics (from "Physics 101") Flashcards

1
Q

Define:

instantaneous velocity (vo).

A

Instantaneous velocity is the direction and magnitude of the rate of change for distance per unit time.

vo = **Δx / t**

or: vo = p/m

Where p is the object’s momentum and m is its mass.

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2
Q

Define:

average velocity (vave)

A

Average velocity is the total distance and direction traveled from an initial position, divided by the total time.

vave = Δxtotal / Δttotal

or: vave = (vf + vi)/2

Note: the second equation assumes constant acceleration, which is also assumed on the AP exam unless specified otherwise.

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3
Q

Define:

acceleration

A

Acceleration is the rate at which velocity changes per unit of time.

**a = Δv / **t

or: a = Δx / t2

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4
Q

What is the acceleration always associated with an object in free fall?

A

9.8 m/s2

This is the acceleration due to gravity, commonly called g. On the AP exam, any falling object is assumed to be in free fall (no air resistance) unless told otherwise.

Note: while it’s convenient to use 10 m/s2 for calculations, the AP exam expects you to still choose the correct answer mathematically.

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5
Q

Describe Newton’s first law of motion.

A

aka the Law of Inertia: An object in motion will continue with constant velocity unless acted on by a net force.

Similarly, an object at rest will continue to remain at rest until acted on by a net force.

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6
Q

What must be true about the acceleration of an object, if all forces acting on it cancel?

A

The object has zero acceleration.

Since all forces cancel to be zero, there is not a net force and there will not be a change in velocity. If there is no change in velocity, that is the same as no acceleration.

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7
Q

What is the relationship between force, mass, and acceleration in Newton’s second law of motion?

A

Fnet = ma

Note: net force and acceleration are both vectors, and must be pointing in the same direction.

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8
Q

What is the proportional change in force to make an object move with twice its original acceleration?

A

Twice the original force must be applied.

From Newton’s second law, F=ma. Force and acceleration are directly proportional.

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9
Q

How does Newton’s third law of motion describe the forces between two objects?

A

F1on2 = -F2on1

For every force from one object on a second, there is an equal and opposite force from the second back on the first.

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10
Q

What magnitude of force must exist from apple to an orange in free space, if it’s found that there is a force from the orange to the apple of 5N.

A

5N

From Newton’s third law, every force excerted must have an equal and opposite force. The negative sign is already factored in, since the question specified direction.

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11
Q

Define:

Weight

A

Weight is explicitly the force on an object due to gravity. W=mg

Weight if often confused with mass; an object with one weight on Earth will have a different, lesser, weight on the moon, but its mass will remain constant.

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12
Q

Define:

mechanical advantage

A

Mechanical advantage is the multiplication of a force using a mechanical device. A small force exerted over a large distance is transformed into a larger force over a smaller distance.

On the AP exam, mechanical advantage appears primarily in problems including levers.

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13
Q

Define:

the kinetic energy of an object

A

An object’s kinetic energy is the energy resulting from its motion.

Kinetic energy is defined as:

KE = ½mv2

where m is the object’s mass and v is its speed. The units of kinetic energy are Joules, just like all other forms of energy.

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14
Q

Define:

fulcrum and lever arm

A

The fulcrum is the point of an object that remains fixed during rotation.

The lever arm is the distance from the fulcrum where a force is applied, to create rotation around the fulcrum.

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15
Q

Define and give units for:

torque

A

Torque is the ability of a force to create a change in the angular orientation of an object, by rotation about a fulcrum point. Torque can also be thought of as the component of work perpendicular to a lever arm.

The SI unit of torque is the N-m.

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16
Q

Briefly describe the Bohr Theory of the atom.

A

The Bohr Theory states:

  • Electrons can only exist in fixed orbits or energy levels.
  • These energy levels are at specific distances from the nucleus.
  • Any energy emitted/absorbed from/by an atom will be the result of an electron jumping from one energy level to another.
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17
Q

Define:

the atomic number, Z, of an element

A

The atomic number of an element is the number of protons contained within the element’s nucleus.

Atomic number is a characteristic property of an element. For instance, all atoms with 1 proton in their nucleus are hydrogen atoms, regardless of how many neutrons exist in the nucleus.

18
Q

Define:

buoyancy

A

Buoyancy is the tendency of an object to weigh less when partially or fully submerged in a liquid.

Buoyancy is caused by the liquid displaced by the object. The liquid pushes up on the object with a force equal to the weight of the liquid displaced.

19
Q

Define:

surface tension of a fluid

A

Surface tension is the ability of a fluid’s surface to resist an external force.

Surface tension is caused by attractive forces between the molecules of the fluid. It is responsible for the spherical shape of soap bubbles and the ability to skip a stone off the surface of a lake.

20
Q

What is the formula for converting between temperature in Centigrade and Fahrenheit?

A

TF = (9/5)*TC + 32

TF = Fahrenheit Temperature
TC = Celsius Temperature

Some standard conversions to memorize:

  • 32º F = 0º C
  • 77º F = 25º C
  • 212º F = 100º C
21
Q

Define:

a conductor

A

A conductor contains many electrical charges within the medium, and they are relatively moveable.

Common conductors are usually metals with high atomic weight, such as silver, copper, and gold.

22
Q

Define:

an insulator

A

An insulator has few free electrical charges within the medium, and those are difficult to move.

Common insulators are as glass, quartz, rubber and teflon.

23
Q

Define:

a battery

A

An electrical battery (or electrochemical cell) is a device that produces a flow of electrons from anode to cathode.

The necessary electrical energy is created by undergoing redox chemical reactions in the cell.

24
Q

Define:

voltage

A

Voltage (electric potential) is the electrical energy per unit charge necessary to move a test charge against the electric field of a fixed charge.

25
Q

Define:

resistance

A

Resistance is a measure of how difficult it is to pass current through some object. Many factors affect resistance, including: cross-sectional area, length, and general resistivity.

Though all materials have some resistance at room temperature, super-cooled superconductors have a resistance of zero.

26
Q

What must have happened to the voltage supplied to a fixed resistance circuit, if the current suddenly drops to half original?

A

The voltage must have also dropped to half.

From Ohm’s law: V=IR

Since R is held constant, V and I are directly proportional. Halving voltage means current must be halved also.

27
Q

What must have happened to the resistance in a fixed voltage circuit, if the current suddenly doubles?

A

The resistance must have dropped to 1/2 original.

From Ohm’s law: V=IR

Since V is held constant, R and I are inversely proportional. Doubling current means resistance must be halved.

28
Q

What does this symbol stand for in a circuit diagram?

A

This is a battery. Batteries will always have a larger positive terminal (labeled +) and a smaller negative terminal (labeled –).

Conventional current always flows from + to – around the circuit.

29
Q

What does this symbol stand for in a circuit diagram?

A

This is a resistor. Resistors impede current flow and have units of ohms.

30
Q

What does this symbol stand for in a circuit diagram?

A

This is a capacitor. Capacitors store charge and have units of farads.

31
Q

What does this symbol stand for in a circuit diagram?

A

This is a switch. Switches can be open (as shown) so that no current flows around the circuit, or closed so that both dots are connected and current flows.

32
Q

What does this symbol stand for in a circuit diagram?

A

This is the symbol for ground. Ground is the physical end of the circuit path and represents zero current or zero voltage.

If no ground symbol is given, the negative terminal of the battery is assumed to be ground.

33
Q

What is the difference visually between resistors in parallel vs. series in a circuit?

A

Resistors in parallel are each on a diverging circuit pathway. A single charge will pass through either one or the other to complete the circuit. (first image)

Resistors in series follow each other on continuous circuit pathway. A single charge must go through both to complete the circuit. (second image)

34
Q

What has happened to the capacitance of a fixed voltage circuit, if a dielectric material is inserted between plates of a capacitor and the charge on those plates doubles in order for current to continue to flow?

A

Capacitance will double.

From the formula: C = Q/V

Since V is held constant, Q and C are directly proportional. Doubling charge must mean that capacitance doubles also.

35
Q

Define:

Conductivity

A

Conductivity is the measure of how well a material is able to conduct electric current through it, and is represented by σ (sigma) or κ (kappa).

Conductivity is the inverse of resistivity and will have units of S/m, where S is the SI unit of siemens.

36
Q

Define and give the SI units for:

Power

A

Power is the rate at which energy is transferred per unit time and has SI units of Watts (W), which represents J/s.

37
Q

Define:

AC current

A

AC current (alternating current) periodically reverses direction of flow, creating both positive and negative values.

This is different from DC (direct current), which flows in only one direction and remains always positive.

Note: to make an AC current value into a DC current equivalent, divide the peak AC current by √2, this is known as the RMS factor.

38
Q

Define:

AC Voltage

A

AC voltage (alternating voltage) periodically reverses sign, having both positive and negative values, due to AC current changing direction and sign.

This is different from normal voltage (direct voltage), which remains always positive, due to supposing that current flows in one direction.

Note: to make an AC voltage value into a DC voltage equivalent, divide the peak AC voltage by √2, this is known as the RMS factor.

39
Q

Define and give the formula for:

AC Power

A

AC power (alternating power) is the energy transferred by an alternating current.

This is similar to normal power, the only difference is that all equation variables are the RMS equivalents.

PRMS = IRMS*VRMS
PRMS = I2RMS*R

40
Q

What is the law that governs the reflection of a light ray off a flat surface?

A

θi = θr

The law of reflection states that: light incident on a reflective surface at some angle will bounce off at an equal angle of reflection, as measured from the normal.

41
Q

Define:

refraction

A

Refraction is when a light ray crosses a boundary from one transparent medium to another.

When the light ray changes media it bends either towards or away from the normal, depending on the properties of the respective media.

42
Q

When white light is separated by a prism into its component colors, in what order do they appear?

A

The separated colors are, in order, red, orange, yellow, green, blue, indigo, violet.

This is easily remembered by the mnemonic ROYGBIV (Roy Gee Biv).