Pressure & Pressure Differences in Fluids (AQA GCSE Physics)

A student takes a plastic bottle and makes a small hole near the bottom of the bottle.

She then fills the bottle with water and places the bottle above a sink, as shown in Figure 2.

Figure 2

The student observes that as the volume of water in the bottle decreases, the jet of water leaving the hole travels a shorter distance before hitting the bottom on the sink.

Explain the above observation.

The student carries out some measurements, recording the depth of the water (measured from the bottom of the bottle) and the distance travelled by the water jet.

Her results are given in Table 1 below.

Table 1

Plot a graph of the distance travelled (on the y-axis) against the depth of the water (on the x-axis).

Your graph should include a curve of best fit.

The student notices that when the water level reaches the height of the hole, the distance travelled by the jet becomes zero.

Use your graph to estimate the height of the hole above the bottom of the bottle.

The Dead Sea contains some of the most saline (salty) water on Earth, with a density (on the surface) of around 1250 kg/m³.

State the relationship between the pressure of a liquid, gravitational field strength, density of the liquid and depth.

Calculate the pressure exerted by the water at a depth of 20m.

The gravitational field strength is 10 N/kg.

Show your working and include a unit with your answer.

A pressure gauge sinks to the bottom of the Dead Sea.

On the bottom it gives a reading of 5 000 000 Pa.

Use the above reading to estimate the depth of the Dead Sea.

Show your working and include a unit with your answer.

In actual fact, the actual depth of the Dead Sea is less than the figure calculated from the above pressure.

What does this imply about the average density of the water compared to the figure given at the start of this question?

Table 2 below gives some data showing how atmospheric pressure varies with altitude above sea level.

Table 2

Explain why atmospheric pressure decreases when the altitude increases.

Plot a graph of atmospheric pressure (y-axis) again altitude (x-axis).

Include an appropriate line of best fit.

Commercial aircraft typically fly at altitudes of around 10 km.

Use your graph to estimate the atmospheric pressure at this height.

Atmospheric pressure  =  _____________ kPa

The pressure inside an aircraft is usually kept at around 80 kPa.

The doors to the aircraft have an area of around 2.0 m².

Calculate the resultant force acting on the door at an altitude of 10 km.

Figure 3 shows two of the forces acting on a submerged balloon, which is travelling upwards through water at a constant velocity.

Figure 3

One of the forces acting on the balloon is missing from the diagram.

Add a further labelled arrow to the diagram to show the relative size and direction of this force.

Explain, in terms of pressure, why the water exerts upthrust on the balloon.

Figure 1 shows two containers that store rainwater.

The containers have taps that are joined by a pipe. 

The taps are closed. 

 Figure 1

Figure 2 shows the water levels inside the containers.

 Figure 2

The density of water is 1000 kg / m³.

 Calculate the pressure that the water causes at the base of container T.

Higher Only

When the taps are opened, water flows in the pipe for some time. Figure 3 shows the final water level in container T.

Complete the diagram to show the final water level in container U.

Higher Only

Explain why the water starts to flow and then stops.

Higher Only

Figure 4 shows a piece of equipment to demonstrate pressure in fluids.

The container is made of glass and each section has a different shape.

Water is poured into the container until it reaches the level shown in the left-hand section.

Figure 4

Complete the diagram by drawing the water levels in the other four sections. Explain why the water fills the container in this way.

Figure 1 shows a cylindrical container which has a base of diameter of 0.15 m and is filled with water to a depth of 0.35 m.

Figure 1

The mass of the water is 6.2 kg.

Calculate the weight of the water in the container.

Calculate the pressure due to the liquid on the base of the container. State the unit.

The water-filled cylinder is placed on a laboratory bench.

Suggest why the total pressure on the bench is higher than the value calculated in part (b).

Higher Only

A bead of hollow glass is dropped into the water and comes to rest floating 12 cm above the base of the cylinder as shown in Figure 2.

Calculate the total pressure on the bead.

Atmospheric pressure at sea level = 1.01 × 10⁵ Pa

Density of water = 1000 kg/m³

Higher Only

Figure 1 shows a hollow metal cylinder containing air, floating in the sea. The density of the metal used to make the cylinder is greater than the density of seawater.

Figure 1

Explain why the cylinder floats.

The cylinder has a length of 1.8 m. It floats with 1.2 m submerged in the sea. The bottom of the cylinder has a cross-sectional area of cross-section of 0.80 m².

 
The density of seawater is 1020 kg/m³. Calculate the force exerted on the bottom of the cylinder due to the depth of the seawater.  

force = ....................................................... N

Deduce the weight of the cylinder. Explain your answer.

Pressure difference in water can be demonstrated using the apparatus shown in Figure 2. The apparatus is hollow and has three short tubes at different depths. When the tube is completely filled with water, water comes out of all the tubes. 

Figure 2

Complete Figure 2 by drawing the paths of water you would expect to see from the other two tubes. Explain why you have drawn this pattern.