Unit 5 - Solids, Liquids + Gases

Question 1

Units of density

Answer 1

Kg/m3

Question 2

What is pressure?

Answer 2

Pressure is the force acting per unit square of a surface

Question 3

What is the equation for pressure

Answer 3

Force/area

Question 4

What are the units of pressure

Answer 4

N/m2 or Pascals (Pa)

Question 5

Explain the physics behind snow shoes to walk in the snow

Answer 5

Weight is spread over a large area so pressure is small

Question 6

Explain the physics behind stiletto heels being likely to mark floors

Answer 6

The force is divided by a very small surface area, giving a large pressure exerted in the heel

Question 7

Explain the physics behind how walking on sand doesn’t hurt as much as walking on pebbles

Answer 7

Sand spreads out so the total contact area is large, therefore pressure is small

Question 8

Explain the physics behind how it is possible to lie on a bed of nails

Answer 8

Total contact area is large so total pressure is small

Question 9

What is the equation for pressure in water

Answer 9

Pressure = height X density X g

Question 10

Explain what happens in the water bag with holes

Answer 10

Pressure is the same throughout the liquid so water jets act in all directions as when Ayer molecules move they transmit a force to all the molecules around them

Question 11

Explain the physics behind the Cartesian diver

Answer 11

Compressing the bottle increases the pressure in the water, which compresses the air inside the diver. The air now displaces less water so there is less up thrust acting on the diver. The diver takes in more water which increases its weight

Question 12

Explain the physics behind the spouting can

Answer 12

As depth increases the weight of the water above increases. This increases the pressure which pushes the water jet out at greater velocity

Question 13

What happens to particles when the temperature of a substance is increased

Answer 13

Particles gain more kinetic energy (move faster or increased vibrations in a solid)

Question 14

Explain what happens to the particles when a substance changes state

Answer 14

Particles gain enough energy to break free of intermolecular bonds. Separation increases (at constant temperature) volume increases

Question 15

What are the main assumptions of the ‘Kinetic theory of matter’

Answer 15

• everything is made up of small particles
• the sizes particles are different for different materials
• the particles are very hard (incompressible) but the separation can change
• particles are always moving
• particles at the same temp have the same KE so heavier particles move more slowly

Question 16

What is evaporation

Answer 16

When a liquid eventually changes into a gas over time, only some molecules have enough energy to escape attractive forces and these molecules change into a gas

Question 17

How is boiling different to evaporation?

Answer 17

In boiling all particles have sufficient energy to escape (quicker process)

Question 18

What is Brownian motion and what does it show

Answer 18

Constant motion of smoke particles (seen by a microscope) is caused by collisions of air particles which transfer energy. This shows that the motion of air particles is constant and random

Question 19

What is 0 kelvin in degrees Celsius

Answer 19

-273

Question 20

What is meant by absolute zero?

Answer 20

Zero kelvin -273C at absolute zero particles have no KE and so do not move. It is very hard to achieve this temperature and you can not go lower

Question 21

Equation for density

Answer 21

Mass/volume