Forces

Question 1

what are scalars and vectors?

Answer 1

• scalars have magnitude only
• vectors have a magnitude and a given direction

Question 2

how can vectors be represented?

Answer 2

with an arrow
- length of arrow= size of vector
- direction of arrow=direction of vector

Question 3

what are contact and non-contact forces?

Answer 3

• a push or pull that acts on an object due to the interaction with another object
• contact forces – objects are touching eg. friction, air resistance,
• non-contact forces – objects are separated eg. gravitational force, electrostatic force, magnetism

Question 4

what is weight?

Answer 4

force of gravity acting on an object

Question 5

weight equation

Answer 5

W=mg

Question 6

what’s the centre of mass?

Answer 6

the single point where weight acts on an object

Question 7

what is resultant force?

Answer 7

one force that has the same effect as all forces acting on an object

Question 8

work done equation

Answer 8

W=Fs

Question 9

what happens to an object temp is friction acts on it?

Answer 9

temp will rise as work is done against friction

Question 10

force (elastic) equation

Answer 10

F=ke

Question 11

what is the relationship between extension and force?

Answer 11

directly proportional until limit of proportionality isn’t exceeded

Question 12

what is moment?

Answer 12

the turning effect of a force

Question 13

moment equation

Answer 13

M=Fd
d is the perpendicular distance

Question 14

what happens to the moments if an object is balanced?

Answer 14

total clockwise moment equals total anti-clockwise moment

Question 15

what makes up a lever system?

Answer 15

• load
• effort
• pivot

Question 16

how can a lever be used as a force multiplier?

Answer 16

distance between pivot and effort = greater than distance between pivot and load=force applied on load greater than effort force

Question 17

what affects the moment of a gear?

Answer 17

its size
larger gear=slower+larger moment

Question 18

what is a fluid?

Answer 18

a liquid or a gas

Question 19

pressure equation

Answer 19

p=F/A

Question 20

pressure on column of liquid equation

Answer 20

p=hpg

Question 21

where do objects experience more pressure?

Answer 21

at the bottom of a column=resultant force up=upthrust

Question 22

what influences whether an object floats or sinks?

Answer 22

• An object floats when its weight is equal to or less than the upthrust.
• An object sinks when its weight is greater than the upthrust
• The water level in a water container rises when an object is lowered into water given that the object displaces some water:
  -the more the object is lowered into the water, the bigger volume that is displaced, causing a larger up thrust
  -When an object is completely immersed in water, the weight of water displaced is equal to the force of up thrust acting on the object
• A partially (or totally) submerged object experiences a greater pressure on the bottom surface than on the top surface as pressure is proportional to the depth of the object
  The difference in pressure creates a resultant force upwards (upthrust)
• Upthrust is why objects appear to weigh less when immersed in a liquid

Question 23

atmospheric pressure

Answer 23

• The atmosphere gets less dense as you go up
• Air molecules colliding with a surface create atmospheric pressure.
• atmospheric pressure decreases with an increase in height=less air above surface=less weight

Question 24

what are the typical speeds for walking, running and cycling?

Answer 24

walking - 1.5 m/s
running - 3 m/s
cycling - 6 m/s.
car - 10-30 m/s
plane - 200-250 m/s
sound in air - 330 m/s

Question 25

distance equation

Answer 25

s=vt

Question 26

why does an object change its velocity when moving in a circle but go at the same speed?

Answer 26

- velocity is speed in a given direction - if the direction of an object changes its velocity will change even if it goes at the same speed

Question 27

acceleration equation

Answer 27

a=∆ v/t

Question 28

uniform acceleration equation

Answer 28

v²-u²=2as

Question 29

what is the acceleration of an object falling near earth's surface?

Answer 29

9.8 m/s2 (falling freely under gravity)

Question 30

what happens to an object falling through a fluid?

Answer 30

- initially accelerates due gravity - eventually the resultant force will be zero = object will move at its terminal velocity

Question 31

newton's 1st law

Answer 31

- if an object is stationary or moving at a constant velocity, the object remains stationary or moving at a constant velocity unless an unbalanced force acts on it

Question 32

what is inertia?

Answer 32

The tendency of objects to continue in their state of rest or of uniform motion

Question 33

newton's 2nd law

Answer 33

F=ma

Question 34

newton's 3rd law

Answer 34

for every reaction, there's an equal and opposite reaction

Question 35

what is stopping distance?

Answer 35

thinking distance (distance travelled in driver's reaction time)+ braking distance (distance travelled until it brakes)

Question 36

what is the average reaction time?

Answer 36

0.2-0.9s

Question 37

what affects a driver's reaction time?

Answer 37

- fatigue - drugs - alcohol - distractions

Question 38

what affects braking distance?

Answer 38

- adverse road+weather conditions eg. wet or icy - poor vehicle conditions eg. tyres or brakes

Question 39

what happens when a force is applied to brakes?

Answer 39

work done by friction between the brakes and the wheel=reduces Ek of the vehicle+temp of brakes increases

Question 40

what happens to the deceleration of vehicle when it goes at high speed?

Answer 40

greater speed=greater braking force=greater deceleration

Question 41

momentum equation

Answer 41

p=mv

Question 42

what is the conservation of momentum?

Answer 42

In a closed system, the total momentum before an event is equal to the total momentum after the event eg collision or explosion

Question 43

what is the difference between a collision and an explosion?

Answer 43

collision=go same direction explosion=go different directions

Question 44

conservation of momentum equation

Answer 44

m1v1+m2v2=mtotalvtotal

Question 45

how does a change in momentum happen?

Answer 45

when force acts on an object that's moving or can move

Question 46

change in momentum equation

Answer 46

F =m∆v/t rate of change in momentum