# Science - Physics - Forces- P5 Flashcards

what is a vector quantity ?

magnitude and direction

what is magnitude ?

size

give examples of a vector quantity ?

- force
- velocity
- acceleration
- displacement
- momentum

what is a scalar quantity ?

quantities with magnitude

give examples of scalar quantities ?

- speed
- mass
- time
- temperature
- distance

how are vectors represented ?

as an arrow

what does the length of the arrow show in vectors ?

the magnitude

what does the direction of the arrow show in vectors

the direction of the quantity

what is a force ?

a push, pull or twist on an object that is caused by it interacting with something

what is a contact force ?

where 2 objects have to be touching for a force to act

give examples of contact forces

- friction
- tension
- air resistance
- normal contact force

what is a non - contact force ?

where objects do not need to be touching for the force to act

give examples of non - contact forces

- magnetic force
- gravitational force
- electrostatic force

what is an interaction pair ?

a pair of forces that are equal and opposite, and act on 2 interacting objects

give an example of an interaction pair

earth is attracted to the sun

sun is attracted to the earth

what does gravity do to anything that is attracted to a planet/star - big mass ?

- on the surface of a planet it makes all things accelerate
- it gives everything a weight

what is mass ?

the amount of matter in an object

what is weight ?

the force acting on an object due to gravity

what is the force acting on an object caused by ?

gravitational fields

what does the size of the force acting on an object depend on ?

the gravitational field strength

how does gravitational field strength vary with location ?

the closer you are to the mass causing the field, the stronger it is

what does the weight of an object depend on ?

the strength of the gravitational field at the location of the object

does the objects mass change depending on weather its on the earth or the moon ?

no

does the objects weight change depending on weather its on the earth or the moon

yes

why does an object weigh less on the moon than it does on earth ?

the gravitational field strength on the moon is less

what is weight measured in ?

newtons

is weight or mass a force ?

weight

how is weight measured ?

using a calibrated spring balance, e.g, a newtonmeter

what is mass measured in ?

kilograms, with a mass balance

what is the equation for calculating weight ?

weight = mass x gravitational field strength

how is weight and mass directly proportional ?

if the mass increases, the weight will too, and if the mass doubles, the weight will also double

an object weighs 10 kg on Earth, what is its weight ?

gravitational field strength on Earth = 9.8 N/Kg

98 newtons

what is a resultant force ?

a single force that can replace all the forces acting on an object to give the same effect as the original forces acting all together

a car is driving with a driving (accelerating) force of 1000 N, air resistance of 600 N is acting in the opposite direction, what is the resultant force ?

1000 N - 600 N = 400 N

400 N forwards (accelerating)

what is a free body diagram ?

a diagram that shows all the forces acting on an isolated object , the direction in which the forces are acting on and their magnitudes

how are free body diagrams represented ?

the length of the arrows show the magnitude of the force, the direction the arrow is pointed in shows the direction

what can free body diagrams help you with ?

calculating resultant forces

how do you draw scale drawings ?

- draw all the forces acting on an object
- make sure they’re to scale in the correct directions
- draw a straight line from the start of the first force to the end of the last force, which is the resultant force
- measure the length of this line to find the magnitude
- measure the angle to calculate the direction

what are scale drawings used for ?

finding the resultant force acting on an object

what is equilibrium ?

a state which all forces acting on an object equal zero, so the resultant force is zero

what is a balanced force ?

where the resultant force is zero, as the forces are balanced

what happens to objects that have a balanced resultant force ?

they are either stationary or are moving at a constant speed

how can you resolve a force which acts at awkward angles?

- split it into 2 components at right angles
- Then add the horizontal and vertical components
- use grid lines then measure them

what is work done ?

the energy transferred when a force moves an object through a distance

what is the more simple explanation of work done ?

the energy transferred when a force acts on an object

how do you calculate work done ?

work done = force x distance

1 joule of work is done when a force of 1 newton causes an object to move a distance of 1 metre, so what is equal to what ?

1 joule = 1 newtonmetre

work done and energy transferred are what ?

the same thing

give an example of work done/ an energy transfer question

a brick is pushed along rough ground with a total force of 45 N

the brick moves a distance of 1.4 metres

find total energy transferred

a brick is pushed along rough ground with a total force of 45 N

the brick moves a distance of 1.4 metres

find total energy transferred

force = 45 N

distance = 1.4 M

W = 45 x 1.4

= 63 j

what is work done/ energy transferred measured in ?

joules

what happens if an object has been elastically deformed ?

it can go back to its original shape and length after the force has been removed

what happens if an object has been inelastically deformed ?

it doesn’t return to its original shape and length after the force has been removed

what are elastic objects ?

objects which can be elastically deformed

what is the extension of a stretched spring directly proportional to ?

the load or force applied

what does the spring constant depend on ?

the material you are stretching - a stiffer spring has a greater spring constant

what is the limit of proportionality ?

the limit at which if a spring is stretched too far it won’t return to its original shape

on a graph where is the limit of proportionality ?

where the graph curves

if an object is elastically deformed, what energy is transferred ?

all this energy is transferred to the objects elastic potential energy store

what is elastic potential energy store ?

the energy transferred to the spring as its deformed

how can work done in the elastic potential energy store be found ?

by calculating the area under the linear force-extension graph

when investigating springs using masses, what experiment can you do to check for a fair test ?

check the masses are the same mass and a suitable size

how do you setup the investigating springs using masses experiment ?

- using the spring you are testing load it with masses one at a time up to a total of 5 masses
- using the ruler check that the spring extends by the same amount each time
- if adding one of the masses pushes the spring past its limit of proportionality, use smaller masses and replace the spring

how do you carry out the experiment of investigating springs using masses ?

- using a ruler measure the natural length of the spring at eye level
- add a mass to the spring and allow the spring to come to rest
- measure the springs new length
- record the weight added and work out the extension
- repeat this process recording the total weight attached and calculating the total extension each time until you have enough measurements

what is a moment ?

the turning effect of a force

what is a moment given by ?

force x perpendicular distance from the line of action of the force to the pivot

what is the line of action ?

a straight line passing through the point at which force acts and in the same direction as the force

what is the perpendicular distance ?

the distance along the line that makes a right angle with the line action of the force

if the total anticlockwise moment equals the total clockwise moment about a pivot - what does this mean ?

the object is balanced and won’t turn

what are levers ?

things that make it easier for us to do work

what does the amount of force needed to produce a particular moment depend on ?

the distance the force is applied from the pivot

what do levers do ?

increase the distance from the pivot at which the force is applied so less force is needed for the same moment

why are levers known as force multipliers ?

they reduce the force that is needed to get the same moment by increasing the distance

what are gears ?

circular discs with ‘teeth’ around their edges

what do gears do ?

their teeth interlock so that turning one causes another to turn in the opposite direction, they are used to transmit the rotational effect of a force from one place to another

what can different sized gears be used for ?

to change a moment of a force, a force transmitted to a larger gear will cause a bigger moment as the distance from edge to the pivot is greater

what will a larger gear do ?

turn slower than a smaller gear

give an example on how gears are used ?

bicycles use gears to transmit the turning effect of the pedals to the back wheel- you can change gear to alter the ratio between how fast you pedal and how fast the wheels turn

what is pressure ?

the force per unit area

what are fluids ?

substances that can flow because their particles are able to move around, either a liquid or gas

what is the unit for pressure ?

pascals Pa

what is density ?

a measure of how close together the particles in a substance are

what is density like in liquids ?

uniform, and doesn’t vary in shape or size

what will a denser liquid have ?

more particles in a given volume

how does pressure increase with density in liquids ?

if a liquid is denser there are more particles to collide so there are more collisions so a higher total force is exerted and there is a higher pressure

what can affect pressure in a liquid ?

depth