topic 5 - forces

Question 1

what is the difference between vectors and scalars

Answer 1

vector quantities have magnitude and direction
scalar only have magnitude

Question 2

give examples of vector and scalar quantities

Answer 2

vector- force, velocity, displacement, acceleration , momentum
scalar - speed , distance, mass , tamperature , time

Question 3

what does the length of a vector arrow show

Answer 3

magnitude

Question 4

what is a contact force and give some examples

Answer 4

when two objects have to be touching for the force to act
e.g. friction , air resistance, tension , normal contact force

Question 5

what is a non contact force and give examples

Answer 5

when objects do not need to be touching for the force to act
e.g. magnetic force, gravitational force, electrostatic force

Question 6

what is an interaction pair

Answer 6

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

Question 7

what are the two important effects of gravity

Answer 7

on the surface of a planet, it makes all things fall towards the ground
it gives everything a weight .

Question 8

how does gravitational field strength vary with location

Answer 8

it is stronger the closer you are to the mass causing the field and stronger for larger masses

Question 9

what is the equation that links mass, weight and gravitational field strength

Answer 9

weight = mass x gravitational field strength

Question 10

what is the relationship between weight and mass

Answer 10

weight and mass are directly proportional

Question 11

what is a resultant force ?

Answer 11

A resultant force is a single force that describes all of the forces operating on a body.

Question 12

what is the equation that links work done distance and force

Answer 12

work done(j) = force(N) x distance (m)

Question 13

how many Nm is one joule

Answer 13

1

Question 14

how do you use scale drawings to find resultant forces

Answer 14

draw all the forces acting on an object , to scale , tip to tail
then draw a straight line from the start of the first force to the end of the last force, - this is the resultant force
measure the length of the resultant force on the diagram to find the magnitude and the angle bearing to find the direction of the force

Question 15

what does it mean if an object is in equilibrium

Answer 15

if all the forces acting on an object combine to give a resultant force of zero
on a scale diagram this means that the tip of the last force you draw should emd where the tail of the first force you drew begins.

Question 16

what three things can applying a force to an object do

Answer 16

may cause it to bend stretch or compress

Question 17

what are the two types of deformation

Answer 17

elastic - it can go back to its originall shape and length after the force has been removed
inelastic - doesnt return to its original shape and length after the force has been removed

Question 18

what is the equation that links force extension and spring constant

Answer 18

force(n) = extension(m) x spring constant (n/m)

Question 19

what is the relationship between force and extension

Answer 19

force is directly proportional to the extension

Question 20

does a greater spring constant mean a stiffer oject or a strechier one

Answer 20

stiffer

Question 21

describe a graph for force against extention

Answer 21

straight line untill it curves at the end
there is a maximum force above which the graph curves showing that extension is no longer proportional to force. this is known as the limit of proportionality
the straight part is elastic deformation
the curve is inelastic

Question 22

describe a practical for investigating the link between force and extension in springs

Answer 22

set up apparatus

pilot experiment to check masses are a good size
1. use an identical spring to the one you will be testing, load it with masses one at a time untill you reach 5 , measure the extension each time
2. work out the increase in the extension of the spring for each of the masses
3. if any cause a bigger increase than the previous masses , you have gone past the limit of proportionality and need to usse smaller masses
.

actual test

1. measure the natural length of the spring with a mm ruler clamped to the stand , take the reading at eye level
2. add a mass to the spring and allow it to come to a rest. record the mass and measure the new length of the spring. the extension is the change in lenght
3. repeat untill you have enough measurements, no fewer than 6
4. plot a force by extension graph of results , it will only curve if you reach the limit of proportionality .

Question 23

what is the area under a force - extension graph equal to

Answer 23

energy in the elastic potential energy store of a stretched spring

Question 24

what is the equaion that links force , moment and distance

Answer 24

moment (Nm) = Force x distance (perpendicular distance)

Question 25

what is a moment

Answer 25

the turning effect of a force

Question 26

how do you get the maximum moment

Answer 26

push at right angles, pushing at any other angle means smaller distance and so smaller moment

Question 27

how do levers make it easier for us to do work

Answer 27

levers increase the distance from the pivot at which the force is applied.
this means less force is needed to get the same moment .

Question 28

describe how gears work

Answer 28

gears are circular disks with teeth around their edges
their teeth interlock so that turning one causes another to turn , in the opposite direction
tjey are used to transmit the rotational effect of a force from one placce to another .
different sized gears can be used to change the moment of the fordce
a force transmitted to a larger gear wil cause a bigger moment as the distance to the pivot is greater.
the larger gear will turn slower than the smaller gear

Question 29

what are fluids

Answer 29

liquid or gas

Question 30

what does it mean when a force is exerted normal

Answer 30

at right angles

Question 31

what is the equation that links area , force normal to a surface and pressure

Answer 31

pressure = force / area

Question 32

describe the density in a liquid

Answer 32

it is uniform ( doesnt change shape or size , the same everywhere

Question 33

how does a more dense liquid increase pressure

Answer 33

the more dense a liquid is , the more particles it has in a certain space, this means there are more particles that are able to collide to the pressure is higher.

Question 34

how does the depth of a liquid increase the pressure.

Answer 34

as the depth of the liquid increasesm the number of particles above the point increases. the weigth of these particles adds to the pressure felt at that point so liquid pressure increases with depth

Question 35

what is the equation that links pressure , height of column of liquid, gravitational field strength and density of a liquid

Answer 35

pressure (Pascals) = H eight x density x gravitational field strength

Question 36

how and why do objects in water experience upthrust

Answer 36

pressure increases with depth so the force exerted on the bottom of the object is larger than the force acting on the top of the object.
this causes a resultant force upwards known as upthrust .
the upthrust is equal to the weight of fluid that has been displaced by the object.

Question 37

why do some objects float and some sink

Answer 37

if the upthrust on an object is equal to its weight , the forces balance and the object floats.
if an objects weight is more than the upthrust the object sinks.

Question 38

how does atmospheric pressure change

Answer 38

as the altitude increases. atmospheric pressure decreases
this is because as the altitude increases, the atmoshpere gets less dense so there are less air molecules that are able to collide with the surface.
there are also fewer air molecules above a surface as the height increases. this means that the weight of the air above it which contributes to atmospheric pressure decreases with altitude