5- FORCES

Question 1

what are vector quantities, give examples, how are vectors represented

what are scalar quantities, give examples

Answer 1

vector quantities-magnitude and direction (force,velocity,displacement, acceleration,momentum)

scalar - magnitude , no direction
(speed distance, mass, temperature, time)

Question 2

how are vectors shown

Answer 2

arrow
length shows magnitude
directin shows direction of quantity
(same speed=same lenght, different velocities due to different directions)

Question 3

what is a force

Answer 3

push or pull on object that is caused by it interacting with something

when two objects interact , the force is produced on both objects

Question 4

what is a contact force

Answer 4

two objects have to be touching for a force to act e.g. friction, air resistance, tension in ropes, normal contact force

Question 5

non contact force

Answer 5

object does not need to be touching for the force to act e.g. magnetic force, gravitational, electrostatic

Question 6

what is an interaction pair

Answer 6

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

Question 7

explain how sun and earth are attracted

Answer 7

by gravitational force, non contact- equal and opposite force of attraction is felt by both sun and earth

Question 8

explain how a chair stays on ground

Answer 8

chair exerts force on ground, ground pushes back at chair with same force - normal contact force.
equal but opposite felt by chair and groudn

Question 9

gravitational force

Answer 9

force of attraction between masses- causes everything to fall to ground and gives everything a weight

Question 10

weight

Answer 10

mass(kg )x gravitationalfield strength(N/kg)

force acting on object due to gravity - the pull of graviational force on object, force caused by gravitational field around earth-

measured in newtons with newtonmeter or calibrated spring balance

weight depends on strength of graviational field at location of object - changes with location

mass and weight are directly proportional

Question 11

gravitational field strength

Answer 11

varies with location, it is stronger the closer you are to the mass causing the field . it is stronger for larger masses

e,g, something will weigh less on moon than it does on earth

Question 12

resultant force

and how do you calculate it

Answer 12

overall force on a point or object-if a number of forces are acting at a single point - you can replace with a single force

if all forces are acting on same line (parallel ) resultant is found by :
adding those going in same direction - any going in opposite direction = resultant force

Question 13

how is work done & energy transferred when a resultant force moves an object through a distance

Answer 13

1- to make thing move:force must be applied 2- what applies force needs source of energy like fuel/food
3-force does work& energy is transferred from one store to other

(e.g. when pushing object on rough surface, work is done against frictional force, energy goes to kinetic store bc object is moving & thermal due to friction- temp increases)

force x distance is work done
1J=1Nm
one joule of work is done when force of 1N causes displacement of 1m

Question 14

how do u use scale drawings to find resultant force

Answer 14

1- draw scale drawing of forces acting (first force to the end of last force)
2- draw resultant force from tail of first arrow to tip of last arrow
3- measure length of resultant with ruler,use scale to find N
4- use protractor to find bearing -clockwisefrom north, 3 digit

Question 15

what is equilibrium

Answer 15

if all forces on object combine to give 0-object is in equilibrium

Question 16

how can you split forces into components

Answer 16

split into 2 components at right angles to each other - horizontal and vertical- - overall has same effect as single force

or draw on scale grid and add components to grid lines, measure

Question 17

how does stretching compressing or bending transfer energy

Answer 17

WORK IS DONE when a force is applied to an object it may stretch compress or bend (more than one force must be acting on object)

(elastic objects)it will be elastically deformed if it returns to original shape + length after force has been removed e.g. spring- energy goes to elastic potential energy store

inelastically deformed-doesnt return to original shape or length after force has been removed- ALL energy to elastic potential energy store

Question 18

explain extension and spring constant

Answer 18

extension is directly proportional to force. the extension of a stretched spring to load/ force applied.

spring constant x extension = force

spring constant depends

Question 18

explain extension and spring constant

Answer 18

extension is directly proportional to force. the extension of a stretched spring to load/ force applied.

spring constant x extension = force

spring constant depends on material you are stretching(stiffer spring= greater spring constant)

Question 19

what is limit of proportionality

Answer 19

the limit to the amount of force you can apply to an objecy for the extension to keep on increasing proportionally

on graph - maximum force is shown where graph curves shows extension is no longer proportional to force

Question 20

practical to investigate link between force and extension

Answer 20

1- measure natural length of spring when no load is applied, with mm ruler clamped to stand - take reading at eye level, - add a marker to bottom of spring to make reading accurate

2-add mass to spring, let it rest, record mass, measure new length of spring (extension is change in length)

3- repeat till you have no fewer than 6

4- plot force-extension graph- it will curve once limit of proportionality has been exceeded(non linear- spring stretches more for each unit increase in force)

(straight line in graph means force & extension is (gradient and spring constant) directly proportional)

Question 21

how to calculate elastic potential energy

Answer 21

0.5 x spring constant x extension

Question 22

what is a moment, how is it calculated

Answer 22

a force/forces cause object to rotate, turning effect of a force is called its moment

moment of force= force x distance

force on spanner causes moment

larger force/distance= larger moment

distance, d, is the perpendicular distance from the pivot to the line
of action of the force, in metres, m.

If object is balanced, total clockwise moment about a pivot= total anticlockwise moment about that pivot.

maxiumum moment= push at right angles (perpendicular) to spanner- other angles mean smaller distnace

Question 23

function of levers

Answer 23

increase distance from pivot where force is applied. = less force is needed to get the same moment
makes it easier to do work(lift load or turn nut)

Question 24

function of gears

Answer 24

transmit rotational effects of force from a place to another circular disks with teeth around edges - teeth interlock so turning gear causes another to turn in opposite direction. different sized gears used to change moment of a force e.g. force transmitted to larger gear = bigger moment= bigger distance to pivot larger gear turns slower than smaller gear

Question 25

what is pressure in a fluid

Answer 25

presure is force per unit area= (PASCALS )particles exert pressure pressure in fluids causes a force normal (at right angles) to any surface in contact with fluid pressure = force normal to a surface/ area of that surface

Question 26

How can The pressure due to a column of liquid can be calculated

Answer 26

pressure = height of the column × density of the liquid × gravitational field strength (density in a liquid is uniform - doesnt vary) density in gas can vary + dense=+ particles=+ weight of particles = +pressure = LIQUID PRESSURE INCREASES WIH DEPTH

Question 27

why do objects in fluids experience upthrust

Answer 27

object is submerged in fluid=pressure of fluid exerts force on it from all directions pressure increases with depth- force exerted on bottom of object is larger than force acting at top of object (= resultant force= upthrust) upthrust= weight of fluid that is displaced by object

Question 28

explain how floating and sinking works

Answer 28

floating: if upthrust on object= objects weight- forces are balanced, object floats sinking;if object is denser than the fluid , unable to displace enough fluid equal to its weight(weight is larger than upthrust) (depends on density )

Question 29

how do submaries make use of upthrust

Answer 29

to sink - large tanks filled with water to increase weight of submarine so it is more than the upthrust to rise-tanks filled with compressed air to reduce weight so its less than upthrust

Question 30

explain how atmospheric pressure works

Answer 30

atmosphere is layer of air around earth. pressure is made by air molecules colliding with earth's surface as altitude increases , atmosphere gets less dense due to less air molecules colliding with surface there are fewer air molecules above surface as height increases so weight of air above it decreases with altitude

Question 31

explain difference between distance and displacement

Answer 31

Distance is how far an object moves.(does not involve direction.)Distance is a scalar quantity. Displacement includes both the distance an object moves(measured in a straight line from the start point to the finish point) and the direction of that straight line. Displacement is a vector quantity

Question 32

explain difference between speed and velocity how do you calculate speed

Answer 32

speed=scalar, velocity=vector speed is how fast youre going but velocity is the speed in a given direction constant speed with changing velocity= speed is same but direction is changing e.g. car on roundabout speed= distance x time

Question 33

typical speeds for everyday objects

Answer 33

person walking- 1.5m/s running-3m/s cycling-6m/s car-25m/s train-55m/s plane-250m/s sound-330m/s

Question 34

how does the speed of different factors vary

Answer 34

speed of person running,walking,cycling varies on age, distance, fitness travelled speed of sound depends on what the sound waves are travelling through speed of wind varies with temperature and atmospheric pressure(& if there is buildings by e.g. forests reduce the speed of air)

Question 35

what is acceleration how is it calculated

Answer 35

acceleration is the change in velocity in a certain amount of time change in velocity/time

Question 36

how to estimate accelerations

Answer 36

1- give a sensible speed for the object/vehicle 2-estimate how long it would take to stop 3-(change in velocity)/ time if it is decelration place a minus sign

Question 37

what is uniform acceleration

Answer 37

also known as constant acceleration -acceleration due to gravity is uniform = 9.8m/s^2 near earth, same gfs final velocity^2 - initial velocity^2 = (2 x acceleration x distance)