Topic 1- General Physics Flashcards
define density (unit)
mass per unit volume of a given object
ρ= density, kg/m^3 m= mass, kg V= volume, m^3 ρ = m/ V
define weight (unit)
Weight is the effect of a gravitational field on a mass
define speed (unit)
distance covered per unit of time (m/s)
The speed of an object is the magnitude of the change of its position; it is thus a scalar quantity.
describe the difference between scalar and vector quantities
vectors have a magnitude and direction
scalars only have a magnitude
give examples of scalar and vector quantities
scalar- distance, speed, mass,
vector- displacement, velocity, weight, acceleration
what is used to measure length
Longer distances- measuring tape (typically to 1cm)
Ruler (to 1mm, eg. 7.4 cm)
Vernier calipers (to 0.1mm, eg. 7.4mm)
Micrometer screw gauge (to 0.01 mm, eg. 7.42 mm)
define acceleration
a= (v-u )/t
or a= Δv/t
acceleration= change in velocity/time
describe difference of displacement and distance
Distance- scalar quantity that refers to “how much ground an object has covered” during its motion.
Displacement- vector quantity that refers to “how far out of place an object is”; it is the object’s overall change in position.
what is g
the acceleration due to gravity (9.8 m/s^2 near Earth)
or gravitational field (9.8 N/kg near Earth)
why is the gravitational pull of different bodies different
Gravitational force is directly proportional to the mass of both interacting objects, more massive objects will attract each other with a greater gravitational force. So as the mass of either object increases, the force of gravitational attraction between them also increases.
describe free fall acceleration
in the absence of air resistance, a free-falling object has an acceleration of 10 m/s/s, downward (on Earth)
what is used to measure length
Longer distances- measuring tape (typically to 1cm)
Ruler (to 1mm, eg. 7.4 cm)
Vernier calipers (to 0.01mm, eg. 7.4mm)
Micrometer screw gauge (to 0.001 mm, eg. 7.42 mm)
what is the zero error
when the measuring instrument registers a reading when there should not be any reading
what is used to measure time
stopwatch
SI base unit and other units for time
base- seconds (s)
1 ms= 10^-2 s
1 µs= 10^-6 s
1 ns = 10^-9 s
how would you accurately measure the thickness of a very thin object (eg. paper) and the mass of a very light object (eg. paper clips)
measure the thickness of multiple sheets/ the mass of multiple clips and divide it by the number
when the acceleration is constant, what will the velocity time graph look like
the velocity will increase as a linear function
for constant acceleration there is linear motion
how would you calculate the distanced travelled for motion with constant acceleration
Calculate the area under a speed-time graph
difference between weight and mass
Weight depends on the gravitational field of the mass, meaning that it can change (N)
Mass is amount of matter in an object and always remains the same (kg)
How can you tell whether an object will float based on density data
Density of object < density of liquid = float
Describe an experiment to determine the density of a liquid and of a regularly shaped solid and make the necessary calculation
Regularly shaped solid:
1. Calculate the volume:
cuboid= lwh
cylinder = π r^2h
- Find the mass using an electric balance
- Divide mass by volume
Liquid
- Pour liquid into measuring cylinder. The level on the scale is the volume.
- Measure the mass of the water with the cylinder then the mass of the cylinder without the liquid. Subtract the latter value from the former.
- Divide mass by volume
Describe the determination of the density of an irregularly shaped solid by the method of displacement
- Lower the solid into a partially filled measuring cylinder. The rise in the level on the volume is the volume of the solid.
- Find the mass of the solid.
- Divide mass by the volume
* if the solid floats, you can add a weight on top to submerge it (remember to subtract its volume from the step 1)
How do you calculate change in velocity from a graph
Find the area under an acceleration graph which represents the change in velocity
what is the difference between speed and velocity
Speed- scalar; rate at which an object covers distance. Velocity- vector; it is direction-aware; rate at which the position changes.
Describe qualitatively the motion of bodies falling in a uniform gravitational field with and without air resistance (including reference to terminal velocity)
- Initially acceleration is g (no/little speed).
- As speed increases, air resistance increases.
- Eventually air resistance is enough to balance weight.
When this happens, velocity reaches its maximum and stays constant.
How can weights (and hence masses) may be compared using a balance
The balance compares the weight, where weight is the downward pull of gravity. The beam balance balances when the downward pull on both pans are equal. However, the masses can also be compared because of the way gravity acts on them.
If the objects on the two pans have the same weight, they have the same mass.
How do you calculate change in velocity from a graph
Find the area under an acceleration graph which represents the change in velocity
Describe qualitatively the motion of bodies falling in a uniform gravitational field without air resistance.
(eg. ball thrown up)
- As ball is thrown upwards, downward (negative) velocity increases by 10m/s each second.
eg. Ball thrown upwards with a velocity of 30m/s, g=10m/s^2
0s= 30m/s, downward velocity is -30m/s 1s= 20m/s, downward velocity is -20m/s 2s= 10 m/s 3s= 0 m/s 4s= 10m/s 5s= 20m/s downward velocity is 20m/s 6s= 30m/s 10m/s is being added to the downward velocity every second
- As ball reaches highest point, downward velocity becomes 0m/s.
- Downward velocity increases by 10m/s each second still as the ball falls.
- Ball eventually has the same speed that it had to begin with, except in the opposite direction.
velocity-time graph line: / across the x axis (eg. from (0,-30) to (6,30)
a negative acceleration is called __?
deceleration
how would you use the dots in ticker tape to describe the motion of a trolley
far apart- faster speed
closer together- slower speed
how would you calculate volume? formula
V=m/p
mass/ density
An object falls at a speed of 𝑥 m/s where air resistance is negligible. How would you calculate the time taken for the object to reach the ground?
acceleration = change in velocity/time a= Δv/t Δv= x-0 (starts with 0m/s) a= 10 m/s^2 in this case the acceleration is g, gravitational field strength
We are trying to find t
t= v/g
in this case time taken (s) = 𝑥 (m/s) ÷ 10 (m/s^2)
An object made of metal A sinks in oil. How would attaching a piece of wood prevent this object from sinking.
The average density of the wood and the object is less than the density of oil
A student has 500 sheets of paper.
The surface area of 1 sheet is 0.063m^2.
1m^2 of the paper has a mass of 0.08kg
What is the mass of one sheet of paper.
ANSWER= Mass of 1 paper is 5.04*10^-3 kg
Divide 0.08kg by the number of sheets in 1m^2
- How many sheets is in 1m^2 of paper?
1 ÷0.063= 15.87 - Divide the mass of 1m^2 of the paper by the number of sheets that makes it up (15.87)
- 08 ÷ 15.87 = 5.04*10^-3
Student A has 500 sheets of paper.
Student B has 5 sheets of paper.
How can student B determine the density of the paper to a similar accuracy? (Additional apparatus may be used)
2pt
They can use electronic calipers/ micrometer to measure the thickness of the paper (in a pile, then divide it by 5)
Then they can use an electronic balance to find its mass
How would you calculate (constant) acceleration from a velocity time graph?
a= Δv/t
Find the velocity on the y axis and divide it by time on the x axis
