cahier physique - physics workbook

1) If you take 1 cm³ of iron ( A small cube) and 1 cm³ of wood, which cube will be lighter (smaller mass ?) ___________
If you measure the mass of 1 cm³ of iron you get 8g. The same volume of oak wood (1cm³) has a mass of 0.7g. We say the density of iron is 8g/ cm³ and the density of wood is 0.7g/ cm³ .
Density is the mass of 1 cm³ of matter.

To find the density of a substance, you need to divide the mass (g) by the volume (cm³).
The mass an be in kg and the volume in m³

3) Read: The models below help you understand why , for the same volume, some material have
a larger mass. Can you see why by observing the models ? Observe also the image below the title
above.

On an atomic level a difference in density can be explained by: The size of the atoms (more nucleons they have, more place they take) and by the way atoms combine together. (they can be close to each other more farther away, depending on the kind of bonds that glue them together)

3) observe the following picture. All the rectangular prisms have the same mass. THey are not made
of the same material so they don't have the same density. What is the difference between them?

density = mass/volume. So if the density increases (metal blocks) and if the mass stays the same,
the volume ___________. If the density decreases (the wood blocks) , and if the mass is constant, the volume _______. We say the density is inversely proportional to the volume.

Here is a table that shows some densities of metal :

Metal	DEnsity	Metal	DEnsity
Aluminum	2.81 g/cm³	Nickel	8.89 g/cm³
Copper	8.97 g/cm³	Platinum	21.40 g/cm³
Gold	19.30 g/cm³	Potassium	0.86 g/cm³
Lead	11.30 g/cm³	Silver	10.50 g/cm³
Lithium	0.54 g/cm³	Sodium	0.97 g/cm³

Which metal has the higher density ? ______________ The lower density ? ______________
If you have 2 cylinders made of these 2 metals having the same mass, with one has the larger volume ? __________

4) You need to learn how to compute the density of different materials.
Here is a video showing you how. (skip brass, go to aluminum 50s) then do the lab.

lab density: find the density of cylinders (metal)

4bis) Here some experiments with cans. get a can of regular coke. If you place the can vertically in the water, is it floating ? horizontally ? what about diet coke ?

5) An object has a mass of 100 grams and a volume of 30 cubic centimeters. WHat is its density?

6) AN object has a mass of 40 000 kilograms and a volume of 5 cubic meters. What is its density>

7) An object has a volume of 3 cubic meters and a density of 6000 kilograms per cubic meter. What is its mass ?

8) lab density of pennies

9) If the density of iron is 8g/cm³, Can you convert to kg/m³ ?
You can do it by steps. (it is like converting the speed mph to m/s).
let's do it once. Then you can memorize the factor. (that is you memorize the multiplication to do)
Understand that 8g/1 cm³ is a fraction, a division. Understand that you can cross out units. (simplify)/

FIRST REMEMBER 1 m³ (a box with 1 m each side) = 1m x 1m x 1m = 100cm x 100cm x 100 cm
so 1 m³ = 1000,000 cm³. Also 1000g = 1kg
(REmember Gulliver lab ? you start with a 1 cm³ cube , you multiply each side by 100 so the volume is multiplied by 100³)

let's convert now . let's get rid of the cm³ and get a m³ and lets get rid of g to get kg.
8g/cm³ = 8g/cm³ x 1,000,000cm³/m³ x kg/1000g = 8,000,000 kg / 1000 m³ = 8,000 g/m³ (cross our the cm³ and the g)

CONCLUSION : to convert g/cm³ to kg/m³MULTIPLY BY 1000 (see above, to go from 8 to 8000 )
to convert kg/m³ to g/cm³ DIVIDE BY 10000. MEMORIZE THAT !
write on index cards: 1 kg/m³ = 1000 g/cm³
Using the same method fill the table below:
(so from left to right you multiply by 1000 and from right to left you divide by 1000)

substance	density g/cm³	density kg/m³
gold (solid)	19
mercury (liquid)		14,000
lead (solid)		11,000
water (liquid)	1
ice (solid)	0.92
air (gas)		1.3
petrol (liquid)	0.8

11) If a liquid or a solid has a density greater than 1, it will rise in water.
If a liquid has a density smaller than 1, it will sink in water.
In the above substance (in the table above), what are the floating substances ?

12) Copy and and complete the table:

object	density (kg/m³)	Mass (kg)	Volume (m³)
A	_________	4000	2
B	8000	______	4
C	2000	1000	______
D	___________	2000	4

I) Which object has the greatest mass?
II) Which has the smallest volume ?
III) which object could be made of the same substance?
IV) Which object object would float on water
(hint: an object float when its density < 1000kg/m³ = density of water)

13) A water tank measured 2m x 4m x 5m. What mass of water will it contain ?

hint: the density of water is 1000kg/m³ or 1g/cm³. you need to find the volume first.

14) To answer the questions use the table below:

Metal	DEnsity	Metal	DEnsity
Aluminum	2.81 g/cm³	Nickel	8.89 g/cm³
Copper	8.97 g/cm³	Platinum	21.40 g/cm³
Gold	19.30 g/cm³	Potassium	0.86 g/cm³
Lead	11.30 g/cm³	Silver	10.50 g/cm³
Lithium	0.54 g/cm³	Sodium	0.97 g/cm³

A) How much does a solid block of aluminum weighs if its dimensions are 4cm by 8cm by 20cm?

hint: You have the density, the volume, solve for the mass (D = M/V)

B) Which weighs more ?:a solid cylinder of gold with a height of 5cm and a diameter of 6cm or a conic cone of platinum with a height of 21cm and a diameter of 8cm? use the formulas:
volume cylinder = пR² x height and volume cone = 1/3(п R² ) x height

hint: first find the volume of each solid. Then find the mass using their density.

C) Chemist Dean Dalton is given a piece of metal and is told that it is sodium. He finds that the metal weighs M= 145.5g .
He places it into a non reactive liquid in a square prism whose base measures 10cm on each edge (W=10cm and L = 10cm)
. If the metal is indeed sodium, how high the liquid level rise (solve for H)

hint: look in the table for the density of sodium d. d=m/V. V = W x L x H. solve for H.

D) A square-prism with a base 5cm (W) by 5cm (L) is partially filled with water. You drop clump of metal that weighs 525g into the container, and the water level rises H= 2cm. What is the density of the metal d ? Assuming tat the metal is pure, what is the metal ? (use table)

hint: d=M/V solve for d. V= W x H x L

15) REVIEW
A) Is the following sentence true or false ?
DEnsity is the amount of mass per unit length: density = mass/length
B) underline the statement that is true.
- density is not mass; it is volume.
- density is a ratio; it is the amount of mass per unit volume.
- density depends on how much of a material you have
- A pure iron nail has the same density as a pure iron frying pan.
C) The density of material depends upon the __________ of the individual atoms that make it up, and the _________ between those atoms.
D) Is the following statement true or false?
A common units of density is grams per cubic centimeters, or g/cm3 ?

16) Professor Messer wants to load some bricks into his van. There are 1000 bricks, and when stacked neatly they measure they measure 2m x 1m x 1m.
A) what is the volume of the stack?
B) What is the volume of one brick?
C) If the density is 2500kg/m³ , what is the mass of the stack?
D) If this van's maximum load is 1000kg , how many bricks can he load ?

17) measuring the ^{density of liquid: lab3}

18) A new plastic is to be made, to be fabricated into little balls that will sink in any liquid whose density is less than 1.20 g/cm³. What is the volume needed in a container to package 500g of this plastic.
hint: suppose the density is at least 1.20 g/cm³ and the mass 500g. solve for the volume. d = m/v

19) Suppose you find an elaborate silver thimble at a flea market. You are not sure if the thimble is solid silver or silver plate. The thimble has a mass of 223g, and you determine that it has a volume of 21.2 cm³. Pure silver has a density of 10.5 g/cm³. Is the thimble solid silver?

20) A nugget appears to be copper. It has a mass of 335grams and a volume of 27.5cm³. Pure copper has a density of 8.96g/cm³. Is the nugget pure copper ?

21) A piece of metal is found in the laboratory. One student says it is a piece of aluminum and another student says that it is a piece of magnesium. The piece of metal has a mass of 425grams and a volume of 244.5cm³. Magnesium has a density of 1.738g/cm³, and aluminum has a density of 2.699g/cm³. What is the composition of the piece of metal?

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