Chapter 3 - Motion

Question 1

What’s the difference between distance and displacement ?

Answer 1

Distance:
- The length of the path moved by an object
- scalar quantity
- SI unit = metre

Displacement:

Question 2

What’s the equation for acceleration ? And is it a vector or scalar quantity ? What’s the SI unit ?

Answer 2

A = v-u/t

It’s a vector

SI = ms-2

Question 3

What’s uniform acceleration ?

Answer 3

This is where the acceleration remains constant over a period of time

Question 4

What’s the acceleration due to gravity ?

Answer 4

g = 9.81 ms-2 downwards

Question 5

What does x equal in v = x / t ?

Answer 5

x = distance

Question 6

What is the gradient of a displacement time graph ?

Answer 6

The gradient = velocity

Question 7

In velocity time graphs, what does gradient = ?

Answer 7

Gradient = acceleration = change in V / change in t

Question 8

In velocity time graphs, Whats the area underneath the curve = ?

Answer 8

The area under the line (curve) = displacement or in a speed time graph it would equal distance

Question 9

What type of quantities are displacement, velocity and acceleration ?

Answer 9

They are all vector quantities so the direction matter as vectors have a magnitude and direction

Question 10

What is speed ?

Answer 10

How fast something is moving, regardless of direction

Question 11

What is displacement ( s ) ?

Answer 11

How far an object has travelled from its starting point in a given direction

Question 12

What is velocity ( v ) ?

Answer 12

It is the rate of change of an objects displacement ( its speed in a given direction )

Question 13

What is acceleration ( a ) ?

Answer 13

The rate of change of a objects velocity

Question 14

What is average speed ?

Answer 14

Its the total distance covered over the total time elapsed

Question 15

What is instantaneous speed ?

Answer 15

The speed of an object in any given point in time is know as instantaneous speed

Question 16

What could acceleration mean ?

Answer 16

Acceleration could mean a change of speed or direction or both

Question 17

What is uniform acceleration ?

Answer 17

It is constant acceleration

Question 18

What are the 4 main equations that are used to solve problems including uniform acceleration ?

Answer 18

v = u + at
s = (u + v) / 2 x t
s = ut + 1/2 at *2
v2 = u2 + 2as

v = final velocity
u = initial velocity
a = acceleration
s = displacement
t = time

Question 19

What is free fall defined as ?

Answer 19

The motion of an object undergoing an acceleration f ‘g’ = 9.81 ms*-2

Question 20

Where does ‘g’ act ?

Answer 20

‘g’ acts vertically downwards

Question 21

What’s the magnitude of ‘g’ ?

Answer 21

unless your given a different value then ‘g’ should be taken as 9.81*-2 though it varies slightly at different points on the earths surface

Question 22

What’s the only force acting on a object when its in free fall ?

Answer 22

weight

Question 23

Can objects have an initial velocity in any direction and still undergo free fall ?

Answer 23

Yes, as long as the force providing the initial velocity is no longer acting on the object

Question 24

What can you replace a with in the equations of motion ?

Answer 24

you can replace a with g

Question 25

what is ‘g’ ?

Answer 25

It is a constant acceleration

Question 26

What are all of the sign conventions ?

Answer 26

g is always downwards so its usually negative

t is always positive

u an v can either be pos or neg

s can be either pos or neg

usually upwards is positive and downwards is negative but you can change this

Question 27

what to do if there is no initial velocity - the object just falls ?

Answer 27

then you put u = 0ms*-1
and then all your equations will be changed a bit because 0 x something is 0

so for e.g.
v = ut + 1/2 at2 becomes v = 1/2 at2

Question 28

Give a method to measure the acceleration due to gravity

what are the sources of error ?

Answer 28

1) measure the height from the bottom of the ball bearing to the trapdoor

2) flick the switch to simultaneously start the timer and disconnect the electromagnet, releasing the ball bearing

3) the ball bearing falls, knocking the trapdoor down and breaking the circuit - which stops the timer

4) use the time measured by the timer and the height between the bottom of the ball bearing and the trapdoor, to calculate a value for g using the formula h = 1/2 gt2

The most significant sources of error will be the measurement of the height - using a ruler you will have a uncertainty of about 1mm

also there is switch delay and air resistance