[forces] pressure
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Pressure
The force per unit area and determines the effect of a force on a surface.
How do flat shoes affect pressure on the ground?
Flat shoes spread the force over a larger area, reducing the pressure.
Why do snow shoes prevent sinking into the snow?
They have a larger area to spread the force, reducing pressure on the snow.
How do high heels affect pressure?
High heels transfer force through a smaller area, causing greater pressure.
How does pressure in fluids act on a surface?
It causes a force normal (at right angles) to the surface.
Formula to calculate pressure on the surface of a fluid:
Pressure (p) = Force (F) / Area (A).
Why does atmospheric pressure decrease with altitude?
Because the number of air molecules decreases, the weight of the air decreases, and there is less air above a surface.
Why must aircraft flying at high altitudes be pressurised?
Because if the air pressure is too low, humans cannot take in oxygen quickly enough to meet their bodies' needs.
What causes atmospheric pressure?
Air molecules colliding with a surface cause atmospheric pressure.
How does pressure in a liquid change with depth?
Pressure increases as the depth increases due to the weight of the column of water above.
Why is the pressure in a liquid greater at the bottom of a dam than near the top?
Because the pressure is due to the weight of the column of water above, which is greater at the bottom.
Why are dam walls usually wedge-shaped?
To withstand greater pressure at the bottom than at the top.
Formula to Calculate Pressure in a Liquid
pressure = height of column × density of the liquid × gravitational field strength
Upthrust
The resultant force upwards on an object submerged in a liquid, due to greater pressure on its bottom surface than on its top surface.
What determines if an object will sink or float?
an object will sink if the upthrust is less than its weight
an object will float if the upthrust is greater than its weight.
Note 
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