Physics CT2

Density and Pressure

Equation for average speed

Average speed = total distance / total time

independant variable

What you change

Dependant variable

What is being measured

Control variable

What stays the same

What do you use a bar chart for?

Discrete data - can only take certain values e.g. shoe size, Categoric data - e.g. type of shoe

What do you use a scatter graph for?

Continues data - can take any value within a range e.g. water temperature

Units for density

kg/m³ , g/cm³ , gm/ml

Equation for density

Density = mass/volume

Symbol for density

ρ

Units for mass

kg or g

Units for volume

cm³, m³, ml, l

What do you measure mass with?

a mass balance/a top pan balance

What do you measure volume with?

Measuring cylinder or measuring cylinder and eureka can

Steps of finding the density of an irregular solid

- Measure Mass

- Measure Volume

- Use the formula d = m/v and substitute with your numbers

- Work out the answer and add the correct units

Eureka can method

- Place the Eureka can on a flat, even surface. Pour water into the can until it just begins to drip out of the spout.

- Wait for the water to stop dripping.

- Place the empty, dry measuring cylinder directly under the spout to catch the displaced water.
- Lower the object into the can. Use a piece of string to gently lower the irregular object into the water. Make sure the object is fully submerged.

- Collect and measure the displaced water. Wait until all the water has finished dripping out of the spout and into the measuring cylinder. The amount of water in the measuring cylinder is the volume of the object.

Precision

Measurements have high precision if repeats are close together

Accuracy

Measurements are accurate if they are close to the true value

Instrument precision

An instrument gives more precise readings if the scale graduations are smaller

How can someone improve their accuracy?

- Choice of method

- Repeat readings

- Measure using larger amounts

How can someone improve their precision?

- Identify the control variables and keep them constant

- Use more sensitive measuring instruments

Equation for pressure

Pressure = Force/Area

Equation for weight

Weight = mass x gravitational field strength

What is the gravitation field strength on earth?

10N/kg

Equation for pressure difference

Pressure difference = height x density x gravitational field strength

What are the units for pressure?

Pascals, kilopascals (1000 pascals), or N/m squared

What are the units for force?

Newtons

What are the units for area?

Metres squared

The pressure in a fluid acts differently or equally in all directions?

Equally

When you go deeper in a fluid the pressure increases or decreases?

Increases

What state of matter(s) are fluids

Liquid and gas

What are fluids

Substances that can flow

Mm to m

divide by 1000

Cm to m

divide by 100

Cm squared to m squared

Divide by 10 000

how to investigate the pressure exerted by a solid object, e.g. the pressure exerted by a human standing on the floor

P=f/a

f=your weight

w=mass x gravitational field strength (g)