P9 Forces

Question 1

vectors vs scalars

Answer 1

vector have magnitude and direction
scalar have only magnitude

Question 2

forces (def)

Answer 2

vector quantities that push/pull an object caused by an interaction with another object

Question 3

contact forces (what + egs)

Answer 3

occur when two objects are touching each other
(friction, air resistance, tension, normal contact force)

Question 4

non-contact forces

Answer 4

act without the two objects touching
(gravitational force, electrostatic force, magnetic force)

Question 5

weight details

Answer 5

• 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

Question 6

free body diagram

Answer 6

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

Question 7

scale (SCALE!) drawings

Answer 7

or draw the parallelogram of forces and find the diagonal

Question 8

resolving forces

Answer 8

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.

Question 9

deformation

Answer 9

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)

Question 10

elastic vs inelastic deformation

Answer 10

elastic: object goes back to its original shape and size when forces are removed (inelastic is just not this)

Question 11

graph of force against extension

Answer 11

gradient = spring constant

extension is directly proportional to force, as long as limit of proportionality is not exceeded

Question 12

Hookes Law (units)

Answer 12

force (N) = sprjng constant (N/m) x extension (m)

F = ke

Question 13

elastic PE

Answer 13

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

Question 14

moment

Answer 14

turning force

= force x distance

Question 15

lever

Answer 15

allows a large moment to produced by allowing force to be applied further from the pivot

Question 16

gears (and transmission of force by them)

Answer 16

A toothed wheel used with other gears to turn axles at different speeds.

number of teeth ∝ radius , radius = perpendicular distance

Question 17

balanced moments

Answer 17

when sum of clockwise moments equals sum of anti-clockwise moments

Question 18

bike gears

Answer 18

low gear (small front gear turning large rear gear):
- wheel turns fewer times per pedal turn
- low speed, but high turning force
- so easier to pedal, used for hills

high gear (large front gear turning small rear gear):
- wheel turns more time per pedal turn
- high speed, but lower turning force
- so harder to pedal, used for high speed