Mass Weight Density

7/28/2019 Mass Weight Density

1/29

Mass, Weight and DensitySec 3 Science Physics


2/29

Mass

Qn: Mass is the(a) same as weight

(b) amount of substance in a body.(c) amount of gravity acting on a body.

Mass is the measure of the amount of

substance in a body.


3/29


4/29

Mass

Mass is measured with

a beam balance or electronic balance.


5/29


6/29

Mass and Inertia

Newton s First Law

A body remains in its state of rest or motion unless it isacted by a resultant force.

A body resists a change in their state of restor motion and the resistance is dependenton its mass.

Inertia is the resistance of a mass to changeits state of motion or rest.

The larger the mass, the larger the inertia.


7/29


8/29

Mass and InertiaQN: What happens to the passengers in a bus if thedriver applies the brake suddenly? Explain your answer.

ANS: The passengers will be thrown forward. Their inertia resist a change in motion hence they will continue to move forward even though the bus hasstopped.


9/29

Gravitational Force

The force that exist between two masses is calledGravitational Force.


10/29

Gravitational force of the Earth

As a result of gravitational force between the Earthand an object, when the object is dropped on earth,

it will fall downwards towards the earth due to thegravitational attraction.


11/29

Gravitational Field

Gravitational field is a region in which amass experiences gravitational force.


12/29

Gravitational Field Strength

Gravitational field strength is thegravitational force per unit mass.

The gravitational field strength on earth is 10 N/g.

That means every 1 kg of mass on earth willexperience 10 N of gravitational force.

The gravitational field strength of the moon is 1/6that of the earth s (i.e. 1.67 N/kg) because moonhas a smaller mass than earth.


13/29

Weight

Weight is the gravitational force acting on abody.

SI unit = Newton (N)

W = mg(W = weight (N), m = mass (kg), gravitationalfield strength (N/kg)


14/29

Weight

Weight of an object is measured using a springbalance or newton meter.


15/29

Weight

Qn: If the mass of your school bag is 8 kg, what is itsweight on earth and on the moon?

On earth - W = mg = 8 x 10 = 80 NOn the moon W = mg = 8 x 10/6 = 13.3 N

Qn: What is the weight of an apple that has a massof 200 g?

W = mg = (200/1000) x 10 = 2 N


16/29

Weight

Qn: Why is there a difference in theperson s weight on the moon and onearth although there is no change in

his mass?

ANS:

The moon has a smaller gravitational

field strength (g).

Since W = mg, the weight of theman on the moon will be smallertoo.


17/29

Weight

Do Q 11 to Q 15 of your notes


18/29

Density

Density of a substance is its mass per unit volume.

SI unit = kg/m 3

Other common unit = g/cm3


19/29

Density

1000 kg/m 3 = 1 g/cm 3

Qn: The density of iron is 7.86 g/cm 3.What is its density in kg/m 3?

Ans: 7.86 g/cm 3 = 7.86 x 1000 = 7860 kg/m 3


20/29

Density

Qn: Do you think the gold bars, gold chain and gold coin have thesame density?

Ans: Yes, the density of a substance is a constant that does notdepend on its shape or volume.


21/29

Density

Glass has a density of 2500 kg/m 3.That means 1 m 3 of glass has a mass

of 2500 kg.

Silver has a density of 10.5 g/cm 3.That means 1cm 3 of silver has a massof 10.5 g.


22/29

DensityQn: The density blocks aremade of different materials butthey have the same volume.How do you determine whichblock has the largest density?

Ans: Density is mass/volumeand their volume are the same,

so the larger the mass, thelarger the density. Measure themass of the blocks, the blockwith the largest mass will havethe largest density.


23/29


24/29

Density

Qn : The density of Olive oil is 0.92 g/cm 3. What is thevolume of 500 g of Olive oil?

Ans: Volume = mass / density = 500 / 0.92 = 544 cm 3

Qn: The mass of an empty beaker is 110 g. The total mass of the beaker is 158 g when 50 cm 3 of a liquid is poured into it.

What is the density of the liquid?

Ans: Density = mass / volume= (158 110) / 50= 48/50= 0.96 g/cm 3


25/29


26/29

DensityWhen 2 liquids of different densities are pouredinto the same container, the denser one will sinkand the less dense liquid will float.

When a solid is placed in a liquid, it will float if itsdensity is lower than the liquid s density, and it willsink if it is denser than the liquid.


27/29

Density

Qn: Why is the woman able tofloat in the dead sea effortlessly?

Ans: The density of dead sea isvery high (due to its high saltcontent) and human body is lessdense than the dead sea henceshe is able to float in the deadsea.

Floating in dead sea
http://www.youtube.com/watch?v=TDEzBWjQpQIhttp://www.youtube.com/watch?v=TDEzBWjQpQI


28/29

Qn: Why does normal coke sink inwater while diet coke floats in water?

Ans: Diet coke contains less sugar thannormal coke hence its density is less.Since it contains a lot of gas, itsdensity will be smaller than that of water and will float.

The Coke Experiment
http://www.youtube.com/watch?v=4wyPPljNdK8http://www.youtube.com/watch?v=4wyPPljNdK8


29/29

Mass

Do Q16 to Q20 of your notes

Mass Weight Density

Documents

Transcript of Mass Weight Density