Unit 1: Motion Flashcards
What are the standard prefixes (SI units) used at the IGCSE level? (scientist will often end up using standard form notation for these)
Deci (d) - /10
centi(c) - /100
milli(m) - /1000
kilo(k) - x1000
mega(M) - x1000000
giga(G) - x1000000000
What are the standard units for measuring length?
1m = 100cm
1m = 1000mm
1km = 1000m
What device do we use to measure things with greater lengths? How can we use this device for thinner things? What is a common fault with it?
- A ruler
- e.g. you want to measure the thickness of a piece of paper. Rather than just measuring one piece of paper (which is too thin for the ruler) you should measure a stack of 500 papers and then divide the total length by 500 to get the thickness of one piece of paper. i.e. you measure several thicknesses and then calculate the average. This same logic can be used to measure the time it takes for a pendulum to complete a single oscillation.
- A common error with rulers is that on their scale before ‘0cm’ there is a small piece of plastic/wood with no measurements, but this piece itself should still be taken into consideration when measuring things.
What device do we use to measure the length of very very small things?
A micrometre screw gauge. These devices give a more precise reading.
Here is a tutorial on how to read from them: https://www.google.com/search?q=how+to+read+a+micrometer+screw+gauge&rlz=1C5CHFA_enSG809SG810&oq=how+to+read+a+micrometer+screw+gauge&aqs=chrome..69i57j0i512l2j0i22i30l5j0i390.10984j0j7&sourceid=chrome&ie=UTF-8&safe=active&ssui=on#kpvalbx=_fzl5YqK4Et2aseMP86C8iAo15
What device is used to measure the volume (of liquids or powders)? What is a common error people make with this device?
- A measuring cylinder
- Remember that liquids often have a meniscus – a curve in the upper surface of the liquid. The volume should be read from the centre of the cylinder, which is often the bottom of the curve (or meniscus).
Here is what I mean: https://drive.google.com/drive/u/0/folders/1Ik2Vxpd6p8qjsU2eOaAeDq21XfOK2tYs
What measurement units do we use for the volume of liquids and solids?
Liquids:
litres (l)
millilitres (ml) - there are 1000 mililetres in a litre
Solids:
cm^3 (one cm^3 is equal to 1 ml)
m^3
- What is an analogue clock?
- What is a digital clock?
- Analogue clocks give time in a continuous manner (smooth waveform)
- Digital clocks give time in a more discrete manner (steps waveform). The order on a digital clock can go hours, minutes, seconds, 1/100 seconds, or milliseconds. Remember that milliseconds do NOT come right after seconds!
What is the definition of speed and what is its unit?
Speed is the distance travelled in a unit of time. Speed is a scalar quantity as it only shows magnitude. It is measured in meters per second (m/s) or kilometres per hour (km/h).
What is the equation relating speed, distance, and time?
Speed = Distance/Time
What is average speed?
Total distance/Total time
What is instantaneuous speed?
The speed of an object at a particular moment in time
How would you calculate velocity? How would you calculate average velocity?
Total displacement / total time taken
It’s just speed but with direction - so it is a vector quantity. So average velocity would be average speed but in a certain direction.
Define velocity
Velocity is the total displacement (change in position) in a unit of time in a stated direction. It is a vector quantity as it shows both a magnitude and a direction.
What is acceleration? What is deceleration?
An increasing rate of speed.
Decreasing rate of speed. When an object is decelerating its acceleration has a negative value.
The concept of acceleration is essentially how quickly speed changes in a given time.
What formula relates acceleration, velocity, and time?
acceleration=change in velocity (m/s) / time taken(s)
a=△v / t
- Note that you can use speed or velocity int his equation
What is the unit for acceleration?
m / s^2
Do you know how to read distance-time graphs? what goes on the x and y axis?
distance = y axis
time = x axis
a straight, sloping line = constant speed
a straight, sloping line of higher gradient = faster constant speed
a flat/horizontal line = stationary (not moving).
Section questions
There are a total of 3 questions
What can you find from the gradient of the line on a distance-time graph?
speed/velocity
How do you read speed (y-axis) vs time (x-axis) graphs?
a flat horizontal line at zero speed = stationary
a flat horizontal line above zero speed = constant velocity
an upward sloping line = accelerating; the steeper the gradient, the higher the acceleration
a downward sloping line = deceleration.
- How do you find the distance travelled from a speed/time graph?
- How do you find acceleration from a speed-time graph
- To find the distance travelled from a speed–time graph, we calculate the area under the line. If the object has constant acceleration, the shape will be a triangle
- The gradient of the line is the acceleration. A straight line on a speed-time graph, indicates a constant acceleration. This means the acceleration has a constant value. A curved line would show the acceleration is changing all the time and is not constant.
What happens to a ball if we drop it down to earth?
If we drop a ball from rest, it immediately speeds up. This is because gravity is pulling the ball downwards. Gravity makes the ball accelerate.
Near to the Earth’s surface, the acceleration of gravity is constant everywhere and is given the letter
‘g’.
So gravity causes things to fall towards the earth at a constant acceleration.
The acceleration of gravity, or the acceleration of free fall, g is equal to an acceleration of 10 m/s 2 .
g = 10 m/s 2
We can use this fact, along with the formula for acceleration, to calculate how fast objects will be falling after a certain time.
What is mass and what is weight?
Mass: The amount of matter in an object. Unit is kg or g etc
Weight: The force acting on an object due to gravity.
We measure mass and weight using a balance.
What unit is used to measure weight?
Newtons (N) - coz it is a force
What equation relates weight and mass?
Weight (N) = Mass(kg) x gravitational field strength(N/kg)
On earth, the gravitational field strength is 10.
On the moon gravitational field strength = 1.6