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
What equation relates density mass and volume?
density (kg/m 3 ) = mass (kg) / volume(m3)
ρ=m / V
How to find the volume of a regularly shaped solid or a liquid
For a regular shape such as the metal block (a cuboid) in Figure 2, find the volume by measuring and multiplying length × width × height.
For a liquid, find the volume using a measuring cylinder (see subtopic P1.1).
To find the mass of a solid or a liquid, use an electronic balance. For a liquid, remember to subtract the mass of the container.
How to find the volume of an irregularly shaped object?
You can find the volume of the pebble using a measuring cylinder or Eureka can.
- Put some water into a measuring cylinder and record its volume.
- Put the pebble into the measuring cylinder of water. The water level will rise. Record the new volume of the water. The difference between your two measurements is the volume of the stone.
- If the pebble will not fit into a measuring cylinder, use a specially designed can called a Eureka can (see Figure 3). As you place the pebble into the can full of water, some water is displaced into a measuring cylinder. The volume of water in the measuring cylinder is equal to the volume of the pebble.
Once you have found the volume of the pebble, find the mass using an electronic balance.
Now calculate the mass,
What can forces do?
change the shape of a body
change the size of a body
increase or decrease the speed of a body
change the direction of motion of a body.
What vocab do you need to know for when there are multiple forces acting on an object?
net force or resultant force. In this case, the movement had to occur. This is an unbalanced force. Unbalanced force leads in an object accelerating.
There could also be balanced forces which ultimately do not cause an object to move. When the forces are balanced and cancel each other out the object is said to be moving at a constant velocity/speed or to be at rest.
essentially:
unbalanced forces = change in speed
balanced forces = constant speed (or the object remains stationary if its speed was zero).
Are forces vector or scalar quantities?
Forces are vectors and have a direction. If they act in the same direction, we add them together. If they act in opposite directions, we subtract to find the difference between the forces.
Often, one of the forces is friction. Friction is a force between two surfaces which impedes motion (makes it more difficult) and always results in heating. If you rub your hands together, the friction between them will produce heat.
What is air resistance?
Consider a ball falling. Gravity pulls the ball downwards but, at the same time, air resistance pushes the ball upwards. Air resistance is basically a force of friction between the air and the object moving through it. The faster the ball moves, the greater the force of air resistance.
what is the equation used to express Hooke’s Law (i.e. the connection between the load force and the extension) is:
force (N) = spring constant (N/m) × extension (m)
F = kx
The spring constant (k) is a given value for a particular spring or wire and tells us how easily the spring or wire stretches. A high number means that a large force is needed to make the spring/wire stretch. The spring constant is measured in N/m (or sometimes N/cm for small extensions).
What is the limit of proprtionality?
If we continue to add more and more force to a spring or wire, it will start to deform or over-stretch. The deformation will show on an extension–load graph as a deviation from a straight line (Figure 6). The point where the deformation begins is called the limit of proportionality. After this point, Hooke’s Law does not apply and the equation is no longer valid.
Graph a stress-strain graph and label all the parts
Answ link: https://drive.google.com/drive/u/0/folders/1snOecmmMYF3sOi1ctOI_dpuZYqE-4cdd
What is the equation to calculate a moment?
Moment (Nm)=Force (N)Distance from pivot(m).
Calculate moment using the product force x perpendicular distance from the pivot.
What is a moment?
Describe the moment of a force as a measure of its turning effect, and give everyday examples.
If you increase the force or distance from the pivot then the moment will be greater.
Example: A spanner is used to screw a nut and bolt into place.
What is the centre of mass?
It is the average position of all the mass in that object. For uniform objects and regular shapes, the centre of mass (sometimes called the centre of gravity) is at a point along the line of symmetry. When an object is suspended from a point, the object will always settle so that its centre of mass comes to rest below the pivoting point
This can be used to find the centre of mass of an irregular shape:
Describe stability in terms of centre of mass:
An object is stable when its centre of mass lies above its base.
If the centre of mass does not lie above its base, then an object will topple over
The most stable objects have a low centre of mass and a wide base. A narrow base with a high centre of masss is the least stable.
What is pressure?
Pressure ( p ) is defined as the force acting on each unit of surface area, or the force per unit area.
What is the equation for pressure?
Pressure (N/m^2) = force / surface area (m^2)
N/m^2 is known as the pascal unit - abbreviated as 1 Pa.
What are the applications of pressure?
- Camels have very big feet to increase surface area to reduce pressure so that they do not sink into the sand. Same logic for skii boards.
- Pins on a pin board. The pin has a very small point, with a very small area. Pressure and area are inversely proportional, so a small area means a large pressure. The pin therefore sinks into a poster board easily.
- Do you know how to find the centre of mass of a regular shape?
- Do you know how to find the centre of mass of an irregular shape by performing and describing an experiment to determine the position of the centre of mass of a plane lamina?
- Draw all lines of symmetry, the point at which they all intersect is the centre of mass.
- Hang lamina from a point. Draw a line down. Keep doing this. You will notice that all these lines intersect at a point. That point is the centre of mass.
When graphing hookes law what goes on the x-axis and what goes on the y-axis?
x-axis: length of extension (in meters)
y-axis: Force applied (in newtons)
Define terminal velocity
As it gains speed, the object’s weight stays the same but the air resistance on it increases. There is a resultant force acting downwards. Eventually, the object’s weight is balanced by the air resistance. There is no resultant force and the object reaches a steady speed – this is known as the terminal velocity.
Why will the center of mass always shift towards the heavier mass?
Center of mass is calculated as weighted average of all points in the geometry of an object, weighted by the mass at those points.
If it were simply an unweighted average, the center would be the geometric center of the space occupied by the object.
Because the points are weightedby the mass they carry, heavier the mass at the points, more importance they get in the final average. And that is how it should be.
Describe the motion of an object when the forces acting on it are in equilibrium
constant speed/rest
Describe the motion of an object when there is a resultant force acting on it
Acceleration
