Physics Unit 2.3
joules (calorie is most commonly used in the U.S.)
since heat energy is in transit, this is the unit used for its measurement
Q = cm∆T (heat added = specific heat x mass x change in temp)
specific heat formula
temperature
the quantity that indicates warmth
kelvin scale
the temperature scale favored by scientists
internal energy
the total of all molecular energies, kinetic plus potential, that are internal to a substance
A Calorie is 1000 calories
(numerically) distinguish between a calorie and a Calorie
4184
1 Calorie = how many joules
4.184
1 calorie (thermal energy) = how many joules
a. 0 b. 1650 kg x m/s (1500 x 1.1) c. 1650 kg x m/s d. 0
1. A 1500-kg car is at rest. You push on it for 30 secs, then let go. While you were pushing it, you made it accelerate to a final speed of 4 km/hr (equal to 1.1 m/s) a. Before you began pushing the car, what was its momentum? b. After you stop pushing the car, what is its momentum c. How much did the car's momentum change? d. What impulse did you deliver to the car?
they're the same bc work is the same
A MiniCooper and a Lincoln Town car are initially at rest on a horizontal parking lot at the end of a steep cliff. For simplicity, we assume that the Town Car has twice as much mass as the MiniCooper. Equal constant forces applied to each car and they accelerate across equal distance. -Which vehicle has the greater kinetic energy at the edge of the cliff? (Think W = ∆KE)
Lincoln town car bc greatest impulse
A MiniCooper and a Lincoln Town car are initially at rest on a horizontal parking lot at the end of a steep cliff. For simplicity, we assume that the Town Car has twice as much mass as the MiniCooper. Equal constant forces applied to each car and they accelerate across equal distance. -Which vehicle has the greater momentum at the cliff's edge? (think Ft = change in mv) Defend your answer
Minicooper
A MiniCooper and a Lincoln Town car are initially at rest on a horizontal parking lot at the end of a steep cliff. For simplicity, we assume that the Town Car has twice as much mass as the MiniCooper. Equal constant forces applied to each car and they accelerate across equal distance. -Which vehicle has the greater acceleration (a = F/m)
they're the same
A MiniCooper and a Lincoln Town car are initially at rest on a horizontal parking lot at the end of a steep cliff. For simplicity, we assume that the Town Car has twice as much mass as the MiniCooper. Equal constant forces applied to each car and they accelerate across equal distance. -Which vehicle has the greater work done on it by the applied force? (Think W = Fd) Defend your answer in terms of the distance traveled.
Lincoln town car bc spends more time on the surface
A MiniCooper and a Lincoln Town car are initially at rest on a horizontal parking lot at the end of a steep cliff. For simplicity, we assume that the Town Car has twice as much mass as the MiniCooper. Equal constant forces applied to each car and they accelerate across equal distance. -Which vehicle has the larger impulse imparted to it by the applied force? (think Impulse = Ft) Defend your answer.
the minicooper (bc greatest acceleration which is inversely proportional to mass)
A MiniCooper and a Lincoln Town car are initially at rest on a horizontal parking lot at the end of a steep cliff. For simplicity, we assume that the Town Car has twice as much mass as the MiniCooper. Equal constant forces applied to each car and they accelerate across equal distance. -Which vehicle lands farther horizontally from the edge of the cliff onto the ground below?
the slower one
A MiniCooper and a Lincoln Town car are initially at rest on a horizontal parking lot at the end of a steep cliff. For simplicity, we assume that the Town Car has twice as much mass as the MiniCooper. Equal constant forces applied to each car and they accelerate across equal distance. -Which vehicle spends more time along the surface of the lot? (the faster or slower one?)
the same (bc mass doesn't affect free fall)
A MiniCooper and a Lincoln Town car are initially at rest on a horizontal parking lot at the end of a steep cliff. For simplicity, we assume that the Town Car has twice as much mass as the MiniCooper. Equal constant forces applied to each car and they accelerate across equal distance. -Which vehicle spends more time in the air, from the edge of the cliff to the ground below?
b, c (Using a liquid with a lower heat capacity than water means that the candle flame will raise the liquid's temperature more quickly than for water. A thicker balloon will conduct heat through to the liquid more slowly, so that the outer part of the balloon wall will heat up more quickly to its melting point.)
Following video (where a balloon w/ just air was popped when it was held over the candle while the baloon w/ water did not pop when held over candle due to water's high specific heat capacity), which of the following changes would make the water balloon more likely to pop? (Ignore effects of convection within the fluid) Choose all that apply a. use a liquid that has a higher heat capacity b. use a thicker balloon c. use a liquid that has a lower heat capacity than water d. use a thinner balloon
B, A, C
From greatest to least, rank the wires in how much they'll sag on a hot summer day. A: Copper, α=17×10−6/∘C B: Aluminum, α=24×10−6/∘C C: Steel, α=11× 10−6/∘C -How much the lengths of various substances change with temperature changes is given by their coefficients of linear expansion, α . The greater the value of α the greater the change in length for a given change in temperature. Three kinds of metal wires, A , B , and C , are stretched between distant telephone poles.
the food is burned and the energy released is measured
How is the energy value of foods determined?
b
I have a small cup of water, and an identical cup full an equal mass of iron. If I allow the same amount of heat to flow into the water and into the iron a) the temperature of the water will increase more than that of the iron b) the temperature of the iron will increase more than that of the water c) the temperature of both the water and the iron will increase by the same amount d) as long as the amounts of heat are the same, neither one will change temperature
the value is less than the heat needed to raise the temperature of the same mass of water through the same temperature difference
If the amount of heat needed to raise the temp. of a 22-kg piece of steel from ⁰C to 100⁰C is 990,000 J, how does this compare w/ the heat needed to raise the temperature of the same mass of water through the same temperature difference?
-Fahrenheit - ice cream is stored in freezers at 26; a hot summer day might be 100 -Celsius- water freezes into ice at 0; liquid water boils at 100; a typical room temperature is 24 -Kelvin- water boils into gas phase at 373.15; the coldest possible temperature is 0
Match the items to the appropriate temperature scale (Fahrenheit, Celsius or Kelvin). -liquid water boils at 100 -ice cream stored in freezers at 26 -the coldest possible temperature is 0 -water boils into gas phase at 373.15 -water freezes into ice at 0 -a hot summer day might be 100 -a typical room temperature is 25
a
Northeastern Canada and much of Europe receive about the same amount of sunlight per unit area. Why, then, is Europe generally warmer in the winter? a. the gulf stream carries warm, high heat capacity water past the west coast of Europe b. the cold ocean absorbs heat from the cold European landmass c. the ocean creates clouds over Europe that act as a blanket d. the low specific heat of frozen tundra in northeastern Canada holds onto its internal energy longer than the thawed soild of Europe
1 Calorie, 1 calorie, 1 joule
Rank the magnitudes of the following units of thermal energy from greatest to least: 1 joule, 1 calorie, 1 Calorie
1/3 as great (Given the same input of energy, the temperature of the metal increased three times as much as the temperature of the water. Therefore, the metal has one-third the heat capacity of water. (Recall that the heat Q delivered to a substance can be written Q= mc ΔT, where m is the mass of the substance and c is its heat capacity.)
Suppose that we replace the aluminum with a mystery metal and repeat the experiment in the video. As in the video, the mass of the metal is the same as that of the water. Room temperature is about 20∘C before the start of the experiment. The water heats up to 40∘C, and the mystery metal heats up to 80∘C. Compared to that of water, the heat capacity of our mystery metal is...
Q= cm∆T = (450 J/kg x ⁰C)(22kg)(100⁰C - 0⁰C) = 990,000 J
The specific heat capacity of steel is 450 J/kg x ⁰C. State the correct equation that shows that the amount of heat needed to raise the temp. of a 22-kg piece of steel from 0⁰C to 100 ⁰C is 990,000 J
b
What do we mean when we talk about Internal energy? a) the temperature of an object b) the amount of thermal energy in an object c) the amount of heat needed to change an object's temperature by 1 degree d) the 'thermal inertia' of a material
c
What do we mean when we talk about the temperature of an object? a) total amount of kinetic energy in an object b) total amount of all 'kinds' of energy in an object c) average kinetic energy per molecule in the object d) average velocity per molecule in the object
food calories
What's the Calorie used to measure
contraction
When the temperature of ice-cold water is increased slightly, does it undergo a net expansion or a net contraction?
liquids generally expand more than solids
Which generally expands more for an equal increase in temperature: solids or liquids?
b
Which one of these represents the largest amount of energy? a) 100 calories b) 1 calorie c) 10 calories d) 5 joules
b
Which one these cites the lowest temperature: a) 273 K b) 270 K c) 32 degrees Fahrenheit d) 0 degrees Celsius
Kelvin (bc only scale that has an absolute zero; F and C do not have absolute zero- both can go into negatives)
You have an object at a specific temperature. Imagine a second object that is twice as hot as the first. If you wanted to figure out the temperature of the hotter object, which would be the easiest temperature scale to use, and why? Farenheit: water freezes at 32 degrees and boils at 212 degrees Celsius: water freezes at 0 degrees and boils at 100 degrees Kelvin: water freezes at 273K and boils at 373K
Q = cm∆T = (1 kcal/kg x ⁰C)(40 kg)(20⁰C) = 800 kcal (heat energy = specific heat capacity x mass x temp. change)
You wish to warm 40 kg of water by 20 degrees Celsius. State the correct equation to show that the amount of heat needed is 800 kcal
(800 kcal)(4.19 kJ/kcal) = 3352 kJ
You wish to warm 40 kg of water by 20 degrees Celsius. The amount of heat needed is 800 kcal. State the correct equation that shows that this is equal to about 3400 kJ
heat
a form of energy associated with the movement of atoms and molecules in any material
temperature
a measure of the average kinetic energy of the particles in a system
temperature
a measure of the average translational kinetic energy per molecule in a substance, measured in segrees Celsius or Fahrenheit or in kelvins (K)
specific heat (capacity)
a sort of thermal inertia bc it signifies the resistance of a substance to a change in its temperature
kinetic energy
all matter- solid, liquid, and gas- is composed of continuously jiggling atoms or molecules and bc of this random motion, the atoms and molecules in matter have this
yes
are thermal energy and internal energy essentially the same thing
specific heat capacity
can be stated as how much internal energy an object can hold before the temperature raises
expand
different substsances ---- at different rates
no, it contains internal energy
does a substance contain heat
no, it contains molecular kinetic energy and possibly potential energy
does matter contain heat
yes, but it doesn't expand in the temperature range between 0 and 4 degrees Celsius
does water, like most other substances, expand when heated
rotational kinetic energy and kinetic energy
energy due to internal movements of atoms within molecules
potential energy `
energy due to the forces between molecules
heat (once transferred, the energy ceases to be heat; an analogy is that work is energy in transit- a body doesn't contain work it DOES work or has work done on it)
energy in transit from a body of higher temperature to one of lower temperature
high
for hand warmers, would you want them to have a high or low specific heat capacity
from higher temp to low temp (this isn't necessarily a flow from a substance with more energy to a substance w/ less internal energy)
for two things in thermal contact, explain direction of heat flow
4.19 joules
how many joules = 1 calorie
add 2 degrees Celsius (starting at 273 K)
how to convert kelvin to Celsius
cold cup
if there's a cold cup of coffee and a warm cup of coffee, in which cup are the molecules moving most slowly in
the one w/ the greater mass
if you have 2 cups of water, and one has 5x as much water as the other one, and they're both the same temperature, which one has more total thermal energy
cup w/ hot water (why the 'mercury' grows upwards in a thermometer when temp. is raised)
if you have a cup of hot water and a cup of cold water, in which cup would you find the molecules more spread out
hot cup
if you have a hot cup of coffee and a cold cup of cofee, in which cup do the KE molecules go faster
paper clip
if you place a steel weight and a paper clip in the oven, which one would be the safest to grab
energy enters your hand bc the stove is warmer than your hand
if you touch a hot stove what happens
the iceberg
if you're comparing an iceberg and a small cup of coffee, which has more thermal/internal energy
liquids; solids
in most cases, the expansion of ---- is greater than the expansion of---
absolute zero
name for in the kelvin scale, when the number 0 is assigned to the lowest possible temperature at which a substance has absolutely no kinetic energy to give up
expand; contract (most thermometers measure temp by means of the expansion or contraction of a liquid)
nearly all materials --- when their temperature is raised and ---- when their temperature is lowered
calorie (the energy ratings of foods and fuels are determined by burning them and measuring the energy released)
the amount of heat required to change the temperature of 1 gram of water by 1 Celsius degree
from a warmer object to a neighboring cooler object
the direction of spontaneous energy transfer
internal energy
the energy associated with the random, disordered motion of molecules
heat
the energy that flows from a substance of higher temperature to a substance of lower temperature, commonly measured in calories or joules
temperature
the equation for this is the amount of kinetic energy/ # of particles
heat
the flow of energy from one thing to another due to temperature difference
internal energy
the grand total of all the energies inside a substance
thermal energy
the internal energy of an object due to the kinetic energy of its atoms and/or molecules
absolute zero
the lowest possible temperature that a substance may have- the temperature at which molecules of the substance have their minimum kinetic energy
calorie
the most common unit of heat in the United States
thermal energy (although scientists prefer the term 'internal energy')
the name for energy that results from heat flow
heat
the name used for energy transferred from one object to another bc of a temp difference between them
specific heat capacity
the quantity of heat per unit mass required to raise the temperature of a substance by 1 Celsius degree
temperature difference between substances and the amount of material (for ex: a barrelful of hot water will transfer more heat to a cooler substance than will a cupful of hot water bc there's more internal energy in the larger volume of water)
the two things that how much heat flows depends on
water
this has a much higher capacity of storing energy than all but a few uncommon materials; a relatively small amount of this absorbs a large quantity of heat for a correspondingly small temperature rise
the specific heat of a substance
this is defined as the quantity of heat required to change the temperature of a unit mass of the substance by 1 Celsius degree
temperature; heat
this is measured in degrees; this is measured in joules
specific heat capacity (the amount of energy needed per gram to raise the temperature of something by 1 degree Celsius; typically measured in calories; water = 1 and Fe = 1/8)
what 'c' indicates
its own temperature
what a thermometer really displays
it increases or decreases
what happens when a substance absorbs or gives off heat
energy transfers from your hand into the colder ice
what happens when you touch a piece of ice
heat energy
what's the calorie used to measure
0; 100
what's the freezing and boiling point in Celsius
32; 212
what's the freezing and boiling point in Fahrenheit
273; 373
what's the freezing and boiling point in Kelvins
Celsius (bc freezing to boiling in Celsius is a 100 degree differnce whereas the freezing to boiling in Fahrenheit is a difference of 180 degrees)
when comparing Celsius to Fahrenheit, is a jump of 1 degree a bigger difference in Celsius or Fahrenheit
its volume increases by nearly 10% and its density is lowered (reason why ice floats on water)
when ice water freezes to become solide ice, what happens to its volume and density
