P9 Forces (UNFINISHED) Flashcards
vectors vs scalars
vector have magnitude and direction
scalar have only magnitude
forces
vector quantities that push/pull an object caused by an interaction with another object
contact forces (what + egs)
occur when two objects are touching each other
(friction, air resistance, tension, normal contact force)
non-contact forces
act without the two objects touching
(gravitational force, electrostatic force, magnetic force)
weight details
- can be considered to act at the object’s centre of mass
- can be measured using a calibrated spring-balance (newtonmeter)
- directly proportional to mass
- = mass x gravitational field strength
free body diagram
use arrows to shoe all of your be forces acting on a single object:
- dot represents objects
- arrow length represents magnitude
- arrow direction represents direction
scale (SCALE!) drawings
resolving forces
the process of breaking down a single force into two perpendicular components
Draw a right-angled triangle to scale, in which each side represents a force. Try to choose a simple scale, for example 1 cm = 1 N.
Measure the lengths of the horizontal and vertical lines. Use the scale for the first line to convert these lengths to the corresponding forces.
deformation
change in the shape of an object caused by stretching, compressing, bending, twisting
multiple forces have to act on a stationary object to deform it (otherwise it would just move)
elastic vs inelastic deformation
elastic: object goes back to its original shape and size when forces are removed (inelastic is just not this)
graph of force against extension
gradient = spring constant
extension is directly proportional to force, as long as limit of proportionality is not exceeded
Hookes Law (units)
force (N) = sprjng constant (N/m) x extension (m)
F = ke
elastic PE
energy is transferred to the elastic potential store when a force stretches or compresses an object (and so does work on it)
= 1/2 k e^2
moment
turning force
= force x distance
lever
allows a large moment to produced by allowing force to be applied further from the pivot
gears (and transmission of force by them)
A toothed wheel used with other gears to turn axles at different speeds.
balanced moments
when sum of clockwise moments equals sum of anti-clockwise moments
