Physics Flashcards
What are examples of scalar quantities?
speed, pressure, energy, and mass
What is the equation for the Y-axis component of a vector?
Y axis component = Magnitude x (sin θ)
What is the equation for the X-axis component of a vector?
X axis component = Magnitude x (cos θ)
Given the X and Y components of a vector, how do you find the resultant magnitude?
Pythagorean Theorem
How do you subtract two vectors?
You make the direction of the vector being subtracted in the opposite direction than it was going. Then you add the two vectors
What is the cross product of A x B?
A x B (sin θ between them)
What is the dot product of A dot B?
A x B (cos θ between them)
How will you remember that the cross product involves the sin θ between the vectors?
The CROSS is where SIN was destroyed
How does the right hand rule apply to the cross product A x B = C?
- Your thumb points in the direction of the first vector (A)
- Your fingers point in the direction of the second vector (B)
- Your palm will now automatically face in the direction of the resultant vector (C)
If a man travels 100 yards east and then 100 yards west, what is his displacement and what is the distance he traveled?
Displacement- 0 yards
Distance- 200 yards
What are the SI units for the velocity of an object?
m/s (meters/ second)
Why will the instantaneous velocity of an object always equal the instantaneous speed?
Because instantaneous velocity is found at a specific moment in time rather than compared to the change in time
What is the equation for the velocity of an object?
V = ΔX/Δt V= displacement/ time
What is a force?
A push or a pull on an object that causes an acceleration of that object
What is the SI unit for force and what are its derived units?
Newton = (kg)(m)/ s^2
Why does the force that gravity exerts on an object decrease as you go higher up on a mountain?
Because the force of gravity is inversely proportional to the distance between the two object’s center of mass
What is the equation for gravitational force?
Fg = Gm1m2/ r^2 Where: G = gravitational force constant m1 = mass of object one m2 = mass of object two r^2 = distance between the two objects center of mass
What is the gravitational force constant and what are its units?
G = 6.67 x 10^-11 (N x m^2/ kg^2)
What is the inequality that describes the force of static friction?
0 ≤ Fs ≤ UsN
Where:
Fs = force of static friction
Us = coefficient of static friction which is different for every surface
N = normal force between the two touching components
What is larger for the surface of sandpaper, the coefficient of static friction or the coefficient of kinetic friction?
Static friction coefficient is always higher
When does kinetic friction play a role in resisting movement between two objects?
When the objects are sliding against each other (ex. sandpaper against wood)
What is the equation for the force of kinetic friction?
Fk = UkN
Where:
Fk = force of kinetic friction
Uk = coefficient of kinetic friction which is different for every surface
N = normal force between the two surfaces
What is the difference between mass (m) and weight (Fg)?
Mass- is the measure of an object’s inertia or its the amount of matter in an object
Weight- is the gravitational force on an object’s mass
What is the equation for the weight of a person?
Fg = mg
Where:
Fg = weight
m = mass of that person
g = gravity that a person is experiencing
(Note the similarities to the equation for force)
What is the equation for the acceleration of an object?
a = ΔV/Δt
What are the SI units for the acceleration of an object?
m/s^2 (meters/ seconds squared)
What is newton’s first law?
If an object with a constant velocity (a = 0) with mass (m) has no force acting upon it (F) then it will remain at rest. This is the law of inertia
What is newton’s second law?
F = ma Where: F = force m = mass a = acceleration (Thus an object needs a forced applied to experience an acceleration)
What is newton’s third law?
The force that one object has on another (A on B) must be equal and opposite to the force that the other object has on it (B on A)
How does jumping while on earth apply to newton’s third law?
Well the force the earth has on us must equal the force that we have on the earth. However, since our mass is far less than earth then we accelerate toward it far faster than it accelerates toward us
What kinematic equation would I use if I was given the initial velocity, acceleration, and reference time, and was then told to find the velocity of the object at that specific time?
V = Vo + at
What kinematic equation would I use if I was given the initial velocity, acceleration, and reference time, and was then told to find how far the object has been displaced from its initial position at that specific time?
X = Vot + at^2/ 2
What kinematic equation would I use if I was given the initial velocity, displacement of the object, and acceleration of the object, and then was told to find the velocity of the object squared?
V^2 = Vo^2 + 2ax
What kinematic equation would I use if I was given the velocity and time and then told to find the displacement of the object at that time?
X = vt
How is terminal velocity reached?
At a certain time after falling, an object’s drag force (created by air resistance) will equal the weight of the object thus its velocity will remain constant
What is the first step to solving projectile motion problems?
Break the resultant vector into its X and Y components
In a projectile motion problem is there acceleration in the X direction? What about the Y direction?
Because there is no constant force in the X direction, there is no acceleration. However, in the Y direction the force of gravity is constant (9.8 m/s^2)
What is the first step in solving an inclined plane problem?
Break the resultant vector into a component that is perpendicular to the plane and a component that is parallel to the plane
In uniform circular motion, where is an object’s instantaneous velocity always pointing?
Instantaneous velocity will always point tangent to the the circular path
What is the force that keeps a car from flying off a racetrack when it goes around a tight turn?
Centripetal Force (always points toward the center of the circle) specifically caused by the friction of the tires in this example
Although not obvious at first, as a car drives in a circular racetrack it is constantly accelerating toward the center of the circle. What is this acceleration called?
Centripetal Acceleration
What is the equation for the force that causes centripetal acceleration?
Fc = mv^2/ r
What is the equation for torque?
t = rf (Sin angle) Where: t = torque r = distance force applied form fulcrum f = force
If all the torques acting on an object cancel out and equal zero then that object is said to be in what?
Rotational Equilibrium
What is energy?
The measure of somethings ability to do work
What is the equation for the energy associated with a moving object?
Kinetic Energy = 1/2 mv^2
Where:
m = mass
v = speed
As an objects mass increases, while its velocity stays the same, what happens to its kinetic energy?
Its kinetic energy increases because the larger size will allow it to do more work
What is the SI unit for energy and what are its derived units?
Joule = kg x m^2/ s^2 = N x m
What does the v stand for in the kinetic energy equation and why is this important?
v = speed and this is important because it shows that the direction an object is traveling does not effect its kinetic energy
What is the equation for gravitational potential energy?
U = mgh Where: m = mass g = acceleration due to gravity h = height above a datum (usually the ground)
What is the equation for elastic potential energy?
U = 1/2 kx^2
Where:
k = spring constant (measure of how stiff a spring is)
x = displacement of spring from equilibrium
When you combine the Potential and Kinetic energies of an object what is the resultant?
The Total Mechanical Energy (E)
When an object undergoes a nonconservative force why can the equation E = U + K NOT be used?
Because a nonconservative force would allow for energy to leave the system via another form (thermal energy, light energy)
When an object undergoes a nonconservative force the object will lose some of its total mechanical energy. Where will this energy be transferred to?
This energy is the work being done by the system
What is work? What are some examples?
Work is the transfer of energy from one form to another (ex. work is done on a piston that converts mechanical energy of steam molecules {pressure} to the movement of whatever the piston is attached to)
What is the equation for work?
W = F * D W = F x D x (cos θ) Where: W = work F = magnitude of force D = magnitude of displacement through which the force is applied
What is the SI unit for work?
Joule
What does the area under a P/V graph for a moveable piston and gas system indicate?
The work being done by the gas. As the gas expands it pushes the piston by changing its volume
For a isobaric process system containing a chamber of gas connected to a piston, is there any work being done by the gas on the piston if gas is added to the chamber?
Yes; because as the volume of the gas increases the piston of the system must move out to keep the pressure of the chamber the same
What is the equation used to find the work done by an isobaric system?
W = PΔV
Where:
P = pressure
ΔV = change in volume of the gas chamber
What is power defined as?
The rate at which work is being done. Thus it is the rate at which energy is transferred from one form to another. (ex. think of lifting a box really fast where you are doing work on the box by changing the chemical energy of your bodies cells into potential energy of the box at a fast rate)
What is the equation for power?
P = W/t
OR
P = ΔE/t
What is the SI unit for power?
Watt = J/s
What is the equation used to connect work to the energy of an object?
The Work-Energy Theorem
Wnet = Kf - Ki
This is seen in your car. As the net work of frictional forces of your brakes add up to cause a change in the kinetic energy of your car
When is it helpful to use the work-energy theorem equation?
When you don’t know the magnitude of the forces or displacement acting on an object
What is the equation for mechanical advantage?
Mechanical Advantage = Fout/ Fin
Where:
Fout = force exerted on an object by a simple machine
Fin = the force applied to the simple machine
Conceptually, what do simple machines actually do?
They make it easier to apply high forces to objects by increasing the distance by which that force is applied
What is the equation to find the efficiency of a simple machine?
Efficiency = Wout/ Win
Where:
Wout = load x load distance
Win = effort x effort distance
What is the relationship between temperature and heat?
Heat (transfer of thermal energy) flows from higher temperature objects to lower temperature ones (ex. from a hot pan to a hand)
What does the zeroth law of thermodynamics state?
That if objects A and B are in thermal equilibrium and objects B and C are in thermal equilibrium, THEN objects A and C are in thermal equilibrium as well meaning that no heat flows between them
What is the freezing point of water in Kelvin?
273 K
What is the freezing point of water in Celsius?
0 °C
What is the freezing point of water in Fahrenheit?
32 °F
What is the boiling point of water in Kelvin?
373 K
What is the boiling point of water in Celsius?
100 °C
What is the boiling point of water in Fahrenheit?
212 °F
What is the typical human body temperature in Celsius?
37 °C
What is the typical human body temperature in Fahreneheit?
98.6 °F
What does the third law of thermodynamics state?
That the temperature of a perfectly organized crystalline object is 0 Kelvin?
What is the equation for thermal expansion? What is the mnemonic for remembering this?
ΔL = αLΔT Where: ΔL = change in length of the object α = the coefficient of linear expansion L = original length ΔT = change in temperature When an solid's temperature changes, its length changes aLOT
What is the equation for the volumetric thermal expansion for a liquid? What is the mnemonic for remembering this?
ΔV = βVΔT Where: ΔV = change in volume of liquid β = coefficient of volumetric expansion V = original volume ΔT = change in temperature When an liquids temperature changes, its volume changes like a Boat
How is an isolated system different from a closed system?
Isolated systems don’t exchange either energy or matter with the surroundings
closed systems don’t exchange matter but do exchange energy with the surroundings
What does the second law of thermodynamics state?
That for every spontaneous process the total entropy of the Universe must increase
What does the first law of thermodynamics state? What is the equation that mathematically shows this?
That when a system loses or gains internal energy, it must be do either to heat/work being done by/on the system ΔU = Q - W Where: Q = energy transferred as heat W = energy transferred as work
In the equation for the first law of thermodynamics, if work is being done by the system what sign (+ or -) will the work term be given? What effect will this have on the total internal energy?
Work will be given a positive value
ΔU = Q - (+W)
The total internal energy will thus decrease
In the equation for the first law of thermodynamics, if work is being done on the system what sign (+ or -) will the work term be given? What effect will this have on the total internal energy?
Work will be given a negative value
ΔU = Q - (-W)
The total internal energy will thus increase
How many joules are in one Calorie?
4,184 Joules
As you touch a hot stove the particles of the stove are directly touching your skin and causing a searing pain. What type of heat transfer occured?
Conduction
On a hot day it feels really nice if you stand in front of a big fan. What type of heat transfer is the fan generating?
Convection
Many cold weather clothing companies have started to put reflective patches on the inside of their jackets. What type of heat transfer are they trying to prevent?
Radiation
What is the measure of the amount of heat transfer required to raise the temperature of a substance by
1 °C
Specific Heat
If you are adding high amounts of heat energy to an object but the temperature is remaining unchanged, what is likely occurring to the substance?
A Phase Change (ice to water)
Given the specific heat of a substance, what equation would help determine how much heat has been gained or lost by that substance?
q = mcΔT
Where:
m = mass of substance
c = specific heat
The particles in a steel beam are moving around very very fast, this object is said to have high what?
Thermal Energy
During the melting of an ice cube to water there is no change in the temperature of the ice cube do to the heat transfer causing an increase in potential energy (more randomness in water). What equation is used to find the heat needed for a substance to undergo a phase change?
q = mL
Where:
m = mass of substance
L = heat of transformation/latent heat
What are the units for the heat of fusion of a substance?
J/Kg (note similarity to specific heat but there is no change in temperature)
What is the process of going from a liquid to a solid called?
Freezing (or solidification)
What is the process of going from a solid to a liquid called?
melting (or fusion)
What is the point at which a substance starts to change from a solid to a liquid
melting point
What is the amount of heat transfer required for a substance to change from a solid to a liquid
Heat of Fusion
What is the amount of heat transfer required for a substance to change between a liquid and a gas?
Heat of Vaporization
What is the equation to find the change in entropy of a substance?
ΔS = Qrev/ T Where: ΔS = change in entropy Qrev = heat gained or lost in a reversible process T = temperature in kelvin
What is the equation for denisty?
p = m/v
Where:
m = mass
v = volume
What are the SI units for density?
Kg/m^3
What is the density of water?
1 g/cm^3
OR
1000 Kg/m^3
What equation can be used to find the weight of any volume of a substance?
Fg = pVg Where: p = density V = volume g = acceleration due to gravity
What is the density (in kg/m^3) of a substance that has a specific gravity of .877?
Specific Gravity = p/ density of water in (g/cm^3)
= 877 kg/m^3
What is the equation for pressure?
P = F/A Where: P = pressure F = magnitude of the normal force A = area force is applied
What is the SI unit for pressure? What are its derived units?
Pascal (Pa) with the units N/m^2
How many pascals are in 1 atm?
101.325 Kilopascals
How many mmHg are in 1 atm?
760 mmHg
How many torr are in 2 atm?
1520 torr
What is the difference between absolute and atmospheric pressure?
The pressure that is pressing down from the atmosphere and changes with elevation. On the other hand, absolute pressure is a measure of the total pressure pushing down on a submerged object
Will a person on top of a mountain experience a higher or lower pressure?
A lower atmospheric pressure
What is the equation for absolute pressure?
P = Po + pgz Where: P = absolute pressure Po = incident or ambient pressure above the liquid p = density of the liquid g = acceleration due to gravity z = depth of the object
How is gauge pressure different from absolute pressure?
Gauge pressure only considers the pressure that exceeds atmospheric pressure (ex. the pressure inside a bike tire)
What is the equation for gauge pressure?
Absolute Pressure - Atmospheric Pressure (note when ambient pressure = 1 atm gauge pressure is pgz)
What does pascals principal state?
That the pressure exerted on an incompressible liquid would be the same everywhere the liquid is touching
What is pascals principal used for in modern machinery?
It is how hydraulic systems work to help machines move big heavy objects (Trac-hoe)