P2 Forces (statics) Flashcards
describe+ name scalar quantities (7)
quantities with a magnitude (size) only
* speed
* distance
* mass
* energy
* temperature
* density
* time
describe+name vector quantities (6)
quantities with a magnitude (length of arrow) and direction
* velocity
* displacement
* weight
* force
* acceleration
* momentum
name all contact forces (7)
- normal contact force
- tension
- friction
- air resistance (normal force of object+air particles)
- water resistance (normal force of object+water particles)
- upthrust (floating - normal force of object+water particles)
- thrust (forwards force eg. car engine)
name all non-contact forces (3)
- gravitational (weight)
- magnetic (N and S)
- electrostatic (+ and -)
name all frictional forces (3)
- friction
- air resistance
- water resistance
describe gravitational force between 2 objects
gravity is an attractive force acting on 2+ objects because of their mass
* as distance between objects increases, force of gravity decreases
* objects with a larger mass exert a larger gravitational force (gravitational force is directly proportional to mass)
* gravitational field strength varies depending on location
define mass
a measure of the amount of matter in an object (kg)
define weight
- the force acting on a single mass/object due to gravity
- depends on its mass and strength of the gravitational field in that area
state the equation for weight
weight = mass x gravitational field strength
W = m x g
(N) (kg) (N/kg)
define centre of mass
the point on an object where the weight of the object acts
why calculate the centre of mass of an object
- centre of mass is the point on an object where the weight of the object acts
1. draw a line from centre of mass to the base
2. if the line is within the base, the object is stable or will not tip over
3. if the line is outside the base, the object will fall over - used to decide whether an object will balance or fall over (+ in which direction)
what effect can the resultant force have on an object (3)
- accelerate (/decelerate)
- deform (change shape/size)
- change direction
describe what could happen to an object when the resultant force = 0N
individual forces are balanced so are at equilibrium
* stationary object remains stationary
* moving object will continue moving at a constant velocity (speed+direction)
describe how to find resultant force from two forces acting at different angles (∠)
- form a parallelogram using dotted lines
- draw a line connecting the point at the initial angle to the point where the dotted lines cross
- the length of this line is the total resultant force (according to scale)
- use a protractor to calculate the direction of force, eg. 8 degrees to the horizontal
state the equation for work done
work done = force x displacement (distance)
W = F x s (d)
(J) (N) (m)
name the 2 units for work done
1 Joule = 1 Newton-metre
-> 1J of work is done when a force of 1N causes a displacement of 1m (W = F x s)
why does work done against frictional forces acting on an object cause it to heat up
kinetic energy store of (moving) object is transferred mechanically/by friction to its thermal energy store
define deformation
what happens to an object when it cannot be made to move (is stationary) and is acted upon by more than one force
define elastic+inelastic deformation (caused by stretching)
- elastic- object returns to its original shape/size once forces are removed
- inelastic- object doesn’t return to its original shape once forces are removed - permanently deformed
name the three types of deformation + the forces involved
- bending
- compressing (compression)
- stretching (tension)
describe the link between force and extension
force is directly proportional to extension
-> provided the limit of proportionality (elastic limit) is not exceeded + the object is not deformed - Hooke’s Law
increasing force will increase extension
state the equation linking force and extension
force = spring constant x extension
F = k x e
(N) (N/m) (m)
state equation calculating work done (elastic potential energy) in stretching a spring
elastic potential energy = 1/2 x spring constant x extension²
Ee = 1/2 x k x e²
(J) (N/m) (m)
method for investigating relationship between force + extension of a stretched spring (RP)
- set up apparatus: clamp+stand on desk, spring+metre ruler hanging over desk, hanging masses attached to end of spring
- measure original length of spring with metre ruler
- add a force of 1N (100g) to the end of the spring
- measure new length of spring, using a marker to take reading from ruler at eye level - minimise parallax error
- calculate extension = new length - original length
- repeat for forces of 2 - 7N
-> also calculate work done using area under the graph or equation for elastic potential energy
