5.1-5.4- density and pressure

Question 1

What is density?

Answer 1

The mass per unit volume of a material

Question 2

What is the link between density and mass?

Answer 2

Objects made from low density materials typically have a low mass and objects from high density materials have a high mass.

Question 3

What is the eq. for Density?

Answer 3

Density = mass/volume
P=M/V

Question 4

What are the approximate densities of different materials?

Answer 4

Air-1.3 (kg/m3)
Wood- 300-8(kg/m3)
Water-1000 (kg/m3)
Granite-2700 (kg/m3)
Lead-11300(kg/m3)

Question 5

What are the equations for the different objects density needs to be found for?

Answer 5

Sphere - 4/3 pie r2
Cube- d3
Cylinder- pie r2 x l

Question 6

Explain the experiment for measuring the density of regularly shaped?

Answer 6

Aim of this experiment is to determine the densities of regular objects using measurements of their dimensions

1- Place the object on a digital balance and note down its mass
2- Use either a rule, Vernier callipers or a micrometre to measure the objects dimensions apparatus depends on the size of the object.
3- repeat these measurements and take an average of these readings before calculating the density

Then calculate the volume of the object
Then work out the density using the equation

Question 7

Explain the experiment for measuring the density of irregularly shaped?

Answer 7

The aim of this experiment is to determine the densities of irregular objects using a displacement technique

Place the object on a digital balance and note down its mass
Fill the eureka can with water up to a point just below the spout
Place an empty measuring cylinder below its spout
Carefully lower the object into the eureka can
Measure the volume of the displaced water in the measuring cylinder
Repeat these measurements and take an average before calculating the density

The volume of the water displaced is equal to the volume of the object
Once the mass and the volume of the shape are known density can be calculated

Question 8

Explain the experiment for measuring the density of Liquids?

Answer 8

The aim of this experiment is to determine the density of a liquid by finding a difference in its mass

Place an empty measuring cylinder on a digital balance and note down the mass
Fill the cylinder with the liquid and note down the volume
Note down the new reading on the digital balance
Repeat these measurements and take an average before calculating the density

Then find the mass of the liquid by subtracting the final reading from the original reading

Mass of liquid = Mass of cylinder with water – mass of cylinder

Question 9

What errors could occour in these experiments for finding densities?

Answer 9

Systematic Errors:

Ensure the digital balance is set to zero before taking measurements of mass
This includes when measuring the density of the liquid – remove the measuring cylinder and zero the balance before adding the liquid

Random Errors:

A main cause of error in this experiment is in the measurements of length
Ensure to take repeat readings and calculate an average to keep this error to a minimum
Place the irregular object in the displacement can carefully, as dropping it from a height might cause water to splash which will lead to an incorrect volume reading

Question 10

What is pressure?

Answer 10

The concentration of a force or the force per unit area

Question 11

Give an example of pressure?

Answer 11

Tractors have large tyres
This spreads the weight (force) of the tractor over a large area
This reduces the pressure which prevents the heavy tractor from sinking into the mud

Question 12

What is the eq. for pressure?

Answer 12

Pressure = Force/Area
P=F/A

Question 13

What creates different levels of pressure?

Answer 13

If a force is spread over a large area it will result in a small pressure
If the force if spread over a small area it will be a large pressure

Question 14

What are fluids?

Answer 14

Liquids or gases

Question 15

How does pressure work for an object immersed in a fluid?

Answer 15

When the object is immersed in a fluid, the fluid will exert pressure squeezing the object. The pressure is exerted evenly across the whole surface of the fluid and in all directions
The pressure exerted in fluids creates a force against surfaces

Question 16

What is the eq. for calculating pressure in a liquid?

Answer 16

Pressure = height x density x gravitational field strenght on earth.

Question 17

How would you increase the pressure of gas in a container?

Answer 17

Heating the container of gas would cause more particle collisions as there would be increased kinetic energy, higher average speed more frequent collisions with the walls of container

Question 18

How would you decrease the pressure in a gas container

Answer 18

Cooling the gas container would cause the particles to have less kinetic energy and a lower average speed eventually they will stop moving the tempreture which this happenes is absolute 0

Question 19

How is pressure effected with depth in a water tube with 3 spouts?

Answer 19

Pressure at the bottom is larger due to the more fluid above. Given this here is more force on the water coming out of the hole which therefore pushes the water further but the area is the same.

Question 20

How can a fish swim deep in the ocean?

Answer 20

Fishes have external forces due to water pressure

Question 21

Why does a sharp knife cut more easily than a blunt one?

Answer 21

Since P=F/A and area for the sharp knife is less than the blunt knife for the same force there will be more pressure underneath the sharp knife.

Question 22

Why is it easier to walk in snow shoes in snow than in regular ones

Answer 22

Since P=F/A and area of the snow shoes is larger than normal ones, for the same force less pressure underneath the shoes.