# Density

Density is a measure of how tight particles are packed in a material. It also governs how 'light' or 'heavy' an object feels to us. It is however best expressed as the following ... OP2 measure mass and volume of a variety of solids and liquids and hence determine their densities

To find Density, what are the tasks to be carried out?

Find the Mass of the object, how ??

Find the Volume of the Object

Mandatory Practical Activity 21

Measure the mass and volume of a variety of solids and liquids and hence determine their densities.

Title

(i) Measure the Mass and Volume of a Variety of Solids

Apparatus

Method Regular solids cube, cuboid, sphere, cylinder, prism,

1. The mass of solids is measured by using a top pan balance.
2. Zero the balance first then place the solid on the pan
3. Record the digital reading of its mass.
4. Measure the dimensions of the regular shaped object, use appropriate formula to calculate the Volume.
5. Use the density formula to calculate the density of the substance

Results

Make out a Table like the one below to figure out the Density of a number of regular solids

Maths

How do you Find the Volume of a regular object ? and density is So Now find the density of the object, do the division V=πr2h

V=4

3πr3 Conclusions

Usual Units of density = g/cm3 or kg/m3 .

try to find the density of; ice, wood, styrofoam, aluminium, glass, iron, brass .....

Finding the Density of an Irregular Solid.

For irregular objects find the mass before you find the volume.

(a) Measuring the Volume of a Small Irregular Solid – use a measuring cylinder.

Pour some water into a measuring cylinder and record the level e.g. 40 cm3 .

Gently lower the solid into the water by a thread until it is completely submerged – if the solid is less dense than water then push it under with a long thin needle.

Record the new higher level of water e.g. 65 cm3 .

Subtract the readings to find the volume of the solid:

65 cm3 - 40 cm3 = 25 cm3 .

Make sure the measuring cylinder was perfectly vertical while taking the readings.

Remember to read from the bottom of the meniscus curve.

(b) Measuring the Volume of a Large Irregular Solid – use an overflow can.

Place an overflow can at the side of a sink with the spout overhanging the sink.

Overfill the overflow can and allow the excess water to flow out – wait till the dripping stops – the water surface is level with the bottom of the opening in the can.

Place a clean dry measuring cylinder under the spout.

Gently lower the solid into the water by a thread until it is completely submerged – if the solid is less dense than water then push it under with a long thin needle.

The displaced water flows out of the can from the spout into the measuring cylinder.

Wait for the dripping to stop.

The volume water in the measuring cylinder is the volume of the solid.

The densities of each of the solids are calculated by dividing their mass by their volume.

Q: Why is it a better idea to find the mass of the object

before finding its volume?

Finding the Density of a Liquid

1ml = 1cm3 .

Measure the Mass and Volume of a Variety of Liquids,

Density Of Water

But before that ......

A two step process is needed to find the mass of a liquid.

First measure and record the

Mass of a clean dry vessel using a top pan balance e.g. 30 g.

Pour the liquid into the beaker and measure the

mass of the beaker plus the liquid 70 g.

By subtraction the mass of the liquid is calculated:

70 g – 30 g = 40 g.

If the volume of the liquid is known then its density can be calculated by dividing the mass of the liquid by the volume of the liquid.

1ml = 1cm3

Mass of Measuring Cylinder before = g

Mass of Measuring Cylinder with water = g

Mass of water = g

Volume of water = cm3

Density of water = g/cm3

The volume of liquids can be determined by using a measuring cylinder and exact volumes of liquid can be delivered by using a pipette or burette.

You might try; oil, methylated spirits, water, diet coke vs coke..

Write out a table of all the Densities that you have found

Investigation Think Topic 1!

Density of Air

Devise an experiment to calculate the Density of Air !

We need to find the Volume and the Mass ....

Can you think how we can complete this investigation.

http://www.nuffieldfoundation.org/practical-physics/measuring-density-air-1

Density of Air

how?

Mass / Volume

Mass of Air ?

How ?

Volume of Balloon

How ?

Fermentation Bin.

Place Balloon in water, make sure it is completly submerged.

Mark water level.

Remove Balloon.

Raise water level up to mark by adding water until the water coincides with the previous mark.

Keep an exact tally of the amount of water added.

By totalling these volumes we find the volume of Air in the Balloon.

Mass / Volume = Density

Remember that 1 ml = 1 cm3

and 1 liter = 1000 ml = 1000 cm3

Investigation Think Topic 2!

What happens when you add Sugar or Salt to water ?

How could you find the density of granular materials, such as sugar or salt?

Some water was placed in a beaker, and its mass was measured using a balance.The mass of water was 200 g. Then 10 g of sugar was weighed out. The sugar was added to the water, and sank to the bottom. 10 minutes later the sugar could not be seen.

Calculate the density of this mix

What is the density of water

what is the density of the sugar ????

What is the density of paper ??

Lead shot, is the projectiles in a shot gun blast. The Lead is made into some small balls, there is some of this in the Lab. How could you find the density of the lead. Make a plan and then try it to get an answer for the density of lead

Helium is the second lightest (least dense) gas after hydrogen (a no-no for modern airships because of its high flammability). By displacing the much denser air around it, the helium-filled envelope makes the airship buoyant. Every kilo of load the ship needs to carry requires a cubic metre of helium to keep it up in the air.

‘It’s a constant battle against weight. Making very small airships is very difficult: you put something on board to make the airship better, but that makes it heavier,’ explains Dorrington, ‘you have to question every gram.’

OP3 investigate flotation for a variety of solids and liquids in water and other liquids, and relate the results of this investigation to their densities

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