Pressure

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수업 노트

Pressure & Forces

Pressure is defined as the force per unit area.
Unit: pascal (Pa) = 1 N/m².
Equation: p = F / A, where p = pressure (Pa), F = force (N), A = area (m²).
A given force over a small area produces a large pressure.
A given force over a large area produces a small pressure.
Example: Tractors have large tyres to reduce pressure and avoid sinking into mud.
Example: Drawing pins have a sharp point (small area) to concentrate force and push into walls.
Example: High heels have a small area, exerting high pressure and sinking into soft ground.

A finger pressing a thumbtack into a surface

Pressure in a Liquid

Pressure in a liquid increases with depth due to the weight of liquid above.
Pressure also increases with density of the liquid.
At the same depth, pressure acts equally in all directions.
Liquid pressure is given by: Δp = ρgΔh (Extended tier only).
Δp = change in pressure (Pa), ρ = density (kg/m³), g = gravitational field strength (N/kg), Δh = change in depth (m).
Total pressure at a depth includes atmospheric pressure (≈ 100 kPa).
Example: A hole at the bottom of a water column produces a stronger jet than one at the top.

Pressure in a liquid increases with depth and acts equally in all directions

Calculating Pressure in Solids

Use p = F / A for solid objects.
Weight (force) = mass × gravitational field strength (W = mg).
Ensure area is in m²; convert cm² to m² by dividing by 10 000.
Worked example: A student of weight 550 N standing on two feet (total area 0.020 m²) exerts pressure = 550 / 0.020 = 27 500 Pa.

Calculating Pressure in Liquids (Extended)

Use Δp = ρgΔh to find pressure difference due to depth.
Example: At 5.0 m depth in water (ρ = 1000 kg/m³, g = 9.8 N/kg), Δp = 1000 × 9.8 × 5.0 = 49 000 Pa.
Total pressure = Δp + atmospheric pressure = 49 000 + 100 000 = 149 000 Pa.
Rearrange: Δh = Δp / (ρg) to find depth from pressure.

Applications of Pressure

High pressure applications: knives, nails, high heels – small area concentrates force.
Low pressure applications: snowshoes, skis, tractor tyres – large area spreads force.
Adding weight (e.g., roof rack) increases pressure on the ground.
Using narrower skis increases pressure on snow.

High heels exert higher pressure than flat shoes because the weight is spread over a smaller area.

Gas Pressure (Extended)

Gas pressure is caused by molecules colliding with container walls.
Increasing temperature increases molecular speed and collision frequency, raising pressure.
Pressure in a gas also varies with depth and density (as a fluid).

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연습 문제

무료 미리 보기 — 43개 중 8개 문제. 가입하면 전부 볼 수 있어요.

1.Pressure is defined as the force per unit _____.
Easy
- Aarea
- Bvolume
- Cmass
- Dlength
2.Which of the following is the correct unit for pressure?
Easy
- Apascal (Pa)
- Bnewton (N)
- Cmetre squared (m²)
- Dkilogram (kg)
3.A tractor has large tyres to reduce the pressure on the ground. This is because pressure is inversely proportional to:
Easy
- Aforce
- Barea
- Cweight
- Dvolume
4.The pressure beneath the surface of a liquid increases with:
Easy
- Adepth and density
- Bdepth only
- Cdensity only
- Dsurface area
5.A drawing pin is pushed into a wall with a force of 50 N. The area of the point is 0.02 cm². What is the pressure exerted by the point on the wall?
Medium
- A2500 N/cm²
- B250 N/cm²
- C25 N/cm²
- D2.5 N/cm²
6.A student of weight 550 N stands on both feet. The total area of his feet in contact with the ground is 0.020 m². What is the pressure exerted on the ground?
Medium
- A27 500 Pa
- B2750 Pa
- C27.5 Pa
- D275 000 Pa
7.A swimmer dives to a depth of 2.0 m in a swimming pool. The density of water is 1000 kg/m³ and gravitational field strength is 10 N/kg. What is the pressure due to the water at that depth?
Medium
- A20 000 Pa
- B2000 Pa
- C200 Pa
- D20 Pa
8.A car of weight 20 000 N has four tyres, each with an area of 0.1 m² in contact with the road. What is the total pressure exerted by the car on the road?
Medium
- A50 000 Pa
- B200 000 Pa
- C5000 Pa
- D20 000 Pa

더 많은 문제

9.A sealed bottle contains air. When the air inside is heated, what happens to the pressure and why?
Medium
- APressure increases because gas molecules move faster and collide more frequently with the walls.
- BPressure decreases because gas molecules move slower and collide less frequently.
- CPressure remains constant because the bottle is sealed.
- DPressure increases because the gas molecules expand.
10.Atmospheric pressure is approximately 100 kPa. A bubble of gas forms 5.0 m below the surface of a lake (density 1000 kg/m³, g = 10 N/kg). What is the total pressure at that depth?
Medium
- A150 kPa
- B50 kPa
- C100 kPa
- D200 kPa
11.A high-heeled shoe exerts a higher pressure on the ground than a flat shoe because:
Easy
- Athe heel has a smaller area, concentrating the force
- Bthe heel has a larger area, spreading the force
- Cthe heel is made of a denser material
- Dthe heel is taller, increasing the weight
12.A manometer measures gas pressure. The liquid in the manometer has density 800 kg/m³. The difference in height between the two columns is 0.15 m. What is the pressure difference? (g = 10 N/kg)
Medium
- A1200 Pa
- B120 Pa
- C12 000 Pa
- D1.2 Pa
13.A student measures the pressure at different depths in a beaker of water. Which graph shows the relationship between pressure and depth?
Medium
- AA straight line through the origin with positive slope
- BA horizontal line
- CA curve that flattens at greater depths
- DA straight line with negative slope
14.A hydraulic lift uses a liquid to transmit pressure. The input piston has an area of 0.01 m² and a force of 200 N is applied. What is the pressure transmitted through the liquid?
Medium
- A20 000 Pa
- B2000 Pa
- C20 Pa
- D2 Pa
15.A diver descends to a depth of 10 m in seawater (density 1025 kg/m³). What is the total pressure on the diver? (Atmospheric pressure = 100 kPa, g = 10 N/kg)
Hard
- A202.5 kPa
- B102.5 kPa
- C200 kPa
- D100 kPa
16.Which of the following is a correct unit for pressure?
Easy
- AN/m²
- BN m
- CN/m
- DN m²
17.A gas bubble at a depth of 5.0 m in a lake has a pressure of 150 kPa. The bubble rises to the surface where atmospheric pressure is 100 kPa. Assuming constant temperature and mass, what happens to the volume of the bubble?
Hard
- AIt increases by a factor of 1.5
- BIt decreases by a factor of 1.5
- CIt stays the same
- DIt doubles
18.A student of weight 550 N stands on one foot. The area of one foot in contact with the ground is 0.010 m². What is the pressure exerted on the ground?
Medium
- A55 000 Pa
- B5500 Pa
- C55 Pa
- D5.5 Pa
19.A hydraulic lift uses a liquid to transmit pressure. The input piston has an area of 0.01 m² and a force of 200 N is applied. What is the pressure transmitted to the output piston?
Medium
- A20000 Pa
- B2000 Pa
- C2 Pa
- D200 Pa
20.In a manometer experiment, the liquid column height difference is 0.20 m. The liquid density is 900 kg/m³. If the atmospheric pressure is 100 kPa, what is the absolute pressure of the gas? (g = 10 N/kg)
Hard
- A101.8 kPa
- B100.18 kPa
- C118 kPa
- D98.2 kPa
21.A student sets up an experiment to compare the pressure exerted by a block on a soft surface. Which factor does NOT need to be controlled?
Easy
- AThe colour of the block
- BThe weight of the block
- CThe area of contact
- DThe material of the surface
22.A student investigates how the pressure in a liquid varies with depth using a pressure sensor. Which of the following should be kept constant?
Easy
- ADensity of the liquid
- BDepth of the sensor
- CVolume of the liquid
- DSurface area of the container
23.Which of the following is the correct definition of pressure?
Easy
- AForce per unit area
- BArea per unit force
- CForce times area
- DMass per unit area
24.What is the SI unit of pressure?
Easy
- APascal
- BNewton
- CJoule
- DWatt
25.A force of 10 N is applied over an area of 2 m². What is the pressure?
Easy
- A5 Pa
- B20 Pa
- C0.2 Pa
- D12 Pa
26.Which of the following exerts the highest pressure on the ground?
Medium
- AA high-heeled shoe
- BA flat shoe
- CA tractor tyre
- DA snowshoe
27.A hydraulic lift uses a liquid to transmit pressure. The input piston has an area of 0.01 m² and a force of 200 N is applied. The output piston has an area of 0.5 m². What is the force exerted by the output piston?
Medium
- A10 000 N
- B10 N
- C1000 N
- D100 000 N
28.Which of the following correctly describes how the pressure in a liquid changes with depth and density?
Easy
- AIt increases with depth and increases with density
- BIt increases with depth and decreases with density
- CIt decreases with depth and increases with density
- DIt decreases with depth and decreases with density
29.In an experiment to investigate pressure in a liquid, a student uses a manometer. The manometer contains a liquid of density 800 kg/m³. The difference in height between the two columns is 0.20 m. What is the pressure difference? (g = 10 N/kg)
Medium
- A1600 Pa
- B160 Pa
- C16 000 Pa
- D1.6 Pa
30.Pressure is a scalar quantity.
Easy
True or false?
31.A drawing pin has a sharp point to create a large pressure. This is because pressure is inversely proportional to:
Easy
- Aforce
- Barea
- Cvolume
- Ddensity
32.A woman of weight 600 N stands on a horizontal floor. The area of her feet in contact with the floor is 0.050 m². What is the pressure she exerts on the floor?
Medium
- A1.2 × 10³ Pa
- B2.4 × 10³ Pa
- C1.2 × 10⁴ Pa
- D2.4 × 10⁴ Pa
33.Which of the following factors does NOT affect the pressure exerted by a liquid?
Medium
- ADepth of the liquid
- BDensity of the liquid
- CVolume of the liquid
- DGravitational field strength
34.At a given depth, the pressure in a liquid acts equally in all directions.
Easy
True or false?
35.Match each application with the reason it reduces or increases pressure.
Medium
- Tractor with large tyres
- Drawing pin with sharp point
- High-heeled shoes
- Large area reduces pressure
- Small area increases pressure
- Small area increases pressure
36.Arrange the following steps in the correct order to calculate the pressure at a depth of 5 m in water of density 1000 kg/m³ (g = 10 N/kg).
Medium
- Write the formula Δp = ρgΔh
- Substitute values: Δp = 1000 × 10 × 5
- Identify ρ = 1000 kg/m³, g = 10 N/kg, Δh = 5 m
- Calculate Δp = 50 000 Pa
37.Select all the factors that affect the pressure exerted by a liquid at a given depth.
Medium
- ADensity of the liquid
- BVolume of the liquid
- CGravitational field strength
- DDepth of the liquid
- ESurface area of the container
38.Complete the sentence:
Easy
Pressure is defined as the ____ per unit area.
39.A force of 200 N is applied to an area of 0.01 m². Calculate the pressure in Pa.
Easy
40.Calculate the pressure due to a column of water of depth 2.0 m. (density of water = 1000 kg/m³, g = 9.8 N/kg).
Medium
41.Explain why a drawing pin is designed with a sharp point.
Medium
42.A force of 200 N is applied to an area of 0.01 m². Calculate the pressure in Pa.
Easy
- A20000 Pa
- B18000 Pa
- C22000 Pa
- D24000 Pa
43.Calculate the pressure due to a column of water of depth 2.0 m. (density of water = 1000 kg/m³, g = 9.8 N/kg).
Medium
- A21560 Pa
- B19600 Pa
- C17640 Pa
- D23520 Pa

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