A2. forces

force

a push or a pull, describes the interaction between bodies

• change the motion of an object – set it in motion or stop it from moving

• change the shape or size of a body

Measured in Newtons, vector

weight (formula)

W = mg

free-body diagrams

F_net = F₁ + F₂

F_net = F₁ - F₂

F_net = (F₁² - F₂²)^1/2

newton’s first law of motion

every object will remain at rest or in uniform motion in a straight line unless compelled to change its state by the action of an external force

newton’s second law of motion

the acceleration of an object depends upon two variables – the net force acting on the object and the mass of the object

newton’s third law of motion

for every action (force) in nature there is an equal and opposite reaction

Electric force

interaction between two charged particles, can be attractive or repelling

Magnetic force

interaction between two poles of a magnetic field, north and south, can repel or attract

Normal force

perpendicular to the surface that an object contacts

Frictional force

A force between two surfaces when in contact. It impedes motion and results in heating

static friction

The frictional force that acts between two bodies rest. μ_s = F /N

dynamic friction

The frictional force that acts between two bodies moving relative to each other μ_dF_n = F

Tension force

The force experienced by a rope (or wire, etc.) attached to a fixed point when the rope is pulled from the other end, or the force experienced by a rope when it is pulled from both ends.

elastic restoring force

The force that counteracts the force extending or compressing a spring and restores the spring to its natural length.

 Hooke’s law

The displacement of a spring is directly proportional to the force exerted on the spring. (F =-kx)

viscous drag force

The resistive force opposing the motion of a body inside a fluid

Buoyancy

The force exerted by a fluid on an object partly or wholly immersed in the fluid, that counteracts the weight of the body.