Forces

Question 1

what is the difference between mass and weight

Answer 1

mass= amount of stuff in an object
same value anywhere in the universe
measured in kg

weight= pull of a gravitational force
weight varies throughout universe (earth 10N/kg, moon 1.6N/kg) measured in N

Question 2

what is the formula relating mass, weight and gravity

Answer 2

weight= mass x gravitational field strength

w= m x good

Question 3

what is the resultant force

Answer 3

overall force on a point or object

there is usually 2 or more forces acting on an object. the overall effect of these forces determine the motion.

you can replace all the forces acting on a single object with one force (as long as the one force has the same effect on the motion of the object)

by adding or subtracting all the forces you can find the overall effect. the overall effect is the resultant force

Question 4

What is Gravitational force

Answer 4

force of attraction between all masses

1. on the surface of a planet it makes all things accelerate towards the ground (all with the same acceleration which is 10m/s^2 on earth)
2. it gives everything weight

Question 5

explain what a reaction force is

Answer 5

if a force is stationary all the forces balance e.g. a teapot on a table

10N is acting on the teapot due to gravity
so the REACTION FOCE must be 10N so the forces are balanced

if there was no reaction force the teapot would accelerate downwards due to the pull of gravity

resultant force on teapot is 0 because 10N-10N =0N

Question 6

what does it mean if there is a resultant force on an object

Answer 6

1. the object will change its motion

aka it causes a change in the objects velocity

Question 7

if there was a car with a driving force is 1000N but a 400N force of air resistance acting on it

what is the resultant force and will the cars velocity change

Answer 7

1000-600= 400N (resultant force)

there is a resultant force so there is always a change in velocity so the car’s velocity will change

Question 8

What are the 3 Laws of Motion

Answer 8

1. object needs a force to start moving
2. no resultant force= no change in velocity
3. resultant force = acceleration

Question 9

explain the law:

an object needs a force to start moving

Answer 9

if the resultant force on a stationary object is 0, the object will remain stationary

a resultant force gets things moving

Question 10

explain the law:

no resultant force means no change in velocity

Answer 10

if there is no resultant force on a moving object, it will just carry on moving at the same velocity.

1. is something moves at a constant velocity the forces on it must be balanced
2. things don’t need a constant overall force to keep them moving
3. to keep things going a steady speed there must be a 0 resultant force

Question 11

explain the law:

a resultant force means acceleration

Answer 11

if there is a non-zero resultant force, then the object will accelerate in the direction of the force

1. resultant force will always produce acceleration or deceleration
2. this ‘acceleration’ can take 5 different forms
   starting
   stopping
   speeding up
   slowing down
   changing direction
3. on a force diagram the arrows won’t be equal

Question 12

what is the formula connecting the resultant force with mass and acceleration

Answer 12

resultant force= mass x acceleration

Question 13

what does ‘reaction forces are equal and opposite mean’

Answer 13

when two objects interact the forces they exert on each other are equal and opposite

1. eg if u push something like a shopping trolley, the trolley will push back against you just as hard
2. when u stop pushing the trolley the trolley stops pushing back against you
3. the two forces are acting on different objects e.g. when u go swimming and you push against water with ur arms the water pushes back at you with an equal force in the opposite direction - SO YOU MOVE

Question 14

what does friction do

Answer 14

slows things down

1. if object has no force propelling it, it will always slow down and stop because of friction
2. friction always acts in opposite directions to movement
3. to travel at a steady speed, the driving force needs to balance the frictional forces
4. friction occurs between 2 surfaces in contact or when an object passes through a fluid (drag)

Question 15

what is resistance or drag from fluids (air or liquid)

Answer 15

most of resistance forces are caused by air resistance, friction or water resistance (drag)

to reduce drag make the object more streamlined or
decrease speed of an object

to increase drag make surface area large eg parachute
or increase the speed of an object (car has more friction when it’s going at 70mph compared to 30mph)

Question 16

what is a terminal velocity

Answer 16

the terminal velocity of an object
is the velocity it reaches when falling at a steady speed ( so the weight is equal to the drag force on the object)

this happens because when an object stars falling the force of gravity is more than the frictional force slowing them down. as the speed increases the friction builds up and reduces the acceleration until the frictional force is equal to the accelerating force. this is when it has reaches its terminal velocity and will fall at a steady speed

Question 17

what does the terminal velocity of falling objects depend on

Answer 17

accelerating force is gravity and would make everything fall at the same rate if it wasn’t for air resistance.

air resistance makes things fall at different speeds and terminal velocity is determined by its drag in comparison to its weight

the drag depends on its shape and area, large surface area =large drag so lower terminal velocity

Question 18

what factors affect your total stopping distance

Answer 18

stopping distance= sum of thinking distance + braking distance

stopping distance of a vehicle is the distance covered in the time between a driver first spotting a hazard and the vehicle coming to a complete stop

1. faster vehicle is going= bigger braking force and greater stopping distance
   but if ur maximum braking force isn’t enough you’ll go further before you stop

Question 19

what is the reaction time

Answer 19

the time between the driver spotting a hazard and taking action

Question 20

what is thinking distance and what is it affected by

Answer 20

thinking distance=distance the vehicle travels during the drivers reaction time

affected by:

1. how fast you’re going - faster=further
2. how dopey you are - tiredness, drugs, alcohol = further

bad visibility and distractions can also be a factor in crashes. it doesn’t affect your thinking distance but if u start thinking about stopping nearer to the hazard - you’re more likely to crash

Question 21

what is the braking distance and what is it affected by

Answer 21

braking distance= distance the car travels under breaking force

affected by:

1. how fast you’re going- faster= further
2. how good your breaks are- worn/faulty= further
3. how good your tyres are - Tyres should have minimum tread depth of 1.6mm in order to get rid of water in wet conditions and prevent aquaplaning
4. how good the grip is of the road surface and weather- icy roads=further