Chapter 3: Force and Pressure

What are some examples of in contact force?

friction, air resistance and tension

Define friction

oppose the motion of an object

Define air resistance

frictional force that is exerted by air of object in motion

Define tension

exerted by a string, rope or spring on an object it is attached to

What are some non-contact forces?

gravitational force, electrostatic force and magnetic force

define gravitational force

The pull of Earth’s gravitational field on an object.

define electrostatic force

attractive or repulsive forces between electric charges.

define magnetic force

attractive or repulsive forces between magnets.

what is mass and the SI unit?

measure of the amount of matter in an object
SI unit: kg

what instrument are used to measure the mass of an object?

beam balance or electronic balance

define weight and state its SI unit

gravitational pull exerted by earth

SI unit: N

what instrument is used to measure the weight of an object?

spring balance or weighing scale

what is the formula for weight?

W = mg

what is the gravitational field strength on moon and earth?

moon: 1.5N/kg
earth: 10N/kg

define density and state its SI unit

mass per unit volume
SI unit: kg/m³

what is the formula for density?

p = m/v

when do object float?

when its density is lower than the density of liquid

when do object sink?

when its density is higher than the density of liquid

define pressure and state its SI unit

force per unit area
SI unit: Pascal (Pa)

does the surface area of an object affect the pressure exerted? how so?

yes! the larger the surface area, the lower the pressure is exerted.

what is the formula for pressure?

p = f/a

define hydraulic press

transfer of pressure using an incompressible liquid in an enclosed cylinder.

is the pressure for each piston equal? How about the force?

yes! however, the force will be different as the area of an object is different.