Ask To Yourself Flashcards
Question & Answer
What is accuracy?
Accuracy is a measure of how close a measured value is to the true (accepted value).
What is random error? And what is the effect of random error?
Random error is chance difference between the observed and true values of something. An error that occurs due to unexpected changes during experiment. These can cause repeated results to differ from one another, effect the precision of the measurement.
What is systematic error? And what is the effect?
Systematic error is consistent of proportional difference between the observed and true values of something. An error occurs due to faults in equipment or experimental method. These can cause the result to differ by the same amount of each time, making them predictable. They can occur due to not calibrating an instrument correctly.
How to reduce the random errors?
- Take at least three repeats and calculate a mean.
- Use computers / data loggers.
- Use higher resolution equipment.
How can systematic error can be reduced?
- Instrument should be recallibrated, or different instruments should be used.
- Corrections or adjustments should be made to the technique.
What is precision?
Precision is how consistent / close together repeat readings are. The closer they are the more precise they are.
What is absolute uncertainty?
Uncertainty given as a fixed quantity. For example, 7 +- 0.6 V
What is the percentage uncertainty in 17 +- 3 A?
3/17 x 100 = 17.647% ~ 18% (2 s.f)
What is factorial uncertainty in 8 +- 0.5 m?
0.5/8 = 1.16
How to reduce percentage and fractional uncertainty?
Measure larger quantities. For example, a longer rope will have a smaller percentage uncertainty that a shorter one.
The time for 10 swings of a pendulum is 13 +- 0.3 s. What is the time and uncertainty for one swing?
1 swing = 13/10 = 1.3 s
uncertainty = 0.3/10 = 0.03 s
Time = 1.3 +- 0.003 s
What is the difference reading and measurement?
Readings are when one value is found, measurements are when the difference between two readings is found.
What is the uncertainty of a thermometer whose smallest division is 5 degree celcius?
The uncertainty in a reading is +- half the smallest division, so uncertainty is +- 5/2 or +- 2.5 degree celcius.
What is the uncertainty in the charge of an electron (1.6 x 10^-19C) ?
The uncertainty in a given values is +- the last significant digit: = 1.6 x 10^-19 +- 0.1 x 10^-19 C
what is the mean and absolute uncertainty of ball to drop are 3.2s, 3.6s, and 3.1s?
Mean = (3.1 + 3.2 + 3.6) / 2 = 3.3 s
Absolute uncertainty = Half the range (3.6 - 3.1) / 2 = 0.25 ~ 0.3s (1 s.f)
3.3 +- 0.3s
what is speed, equation of speed and SI units?
Speed is the rate of change of distance.
The equation = distance / time take
SI units = ms^-1
What is displacement?
Displacement is the distance it has travelled in a given direction, so it is a vector with both magnitude and direction.
What is velocity, equation of velocity, and SI units?
Velocity is rate of change of displacement or speed in a given direction, making velocity a vector.
The equation = change in displacement/time
SI units = ms^-1
What is acceleration, equation of acceleration and SI units?
Acceleration is the rate of change of velocity, making it a vector.
The equation = change in velocity / time
SI units are ms^-2
What is straight, horizontal line represent on a displacement-time graph and velocity -time graph?
Displacement-time : a stationary object.
Velocity-time : An object moving with constant velocity.
What does line with a constant, non-zero gradient represent on displacement-time graph and velocity-time graph?
Displacement-time : an object moving with constant velocity.
Velocity-time : an object that is accelerating (positive gradient of decelerating (negative gradient).
What does curved line represent on a displacement-time graph?
Acceleration (if gradient is increasing) or deceleration (if gradient is decreasing)
What does the area under a velocity-time graph and acceleration-time graph represent?
Velocity-time : Displacement
Acceleration-time : Velocity
Which way does gravity act?
downward
What is free fall?
An object dropped in air experiences no air resistance.
1 kg rock and 10 kg small boulder are dropped from the back of a truck at the same time. Which will hit the ground first?
Both of them dropped at the same time.
What is gravity?
When an object is in free fall.
What is freely falling objects?
Fall with same acceleration, net force acting on them is weight, their weight-to-mass ratios are always the same, their acceleration is g, the acceleration due to gravity.
What factor effects the amount of air resistance experienced by an object?
Surface and speed of object through air.
What is projectile?
Projectile is particle that moves freely under gravity in two-dimensional plane.
What is time of flight of projectile?
The time of flight of projectile is the total time it is in the air.
What is range?
Range is the horizontal distance it travels.
What is maximum height attained by projectile?
The maximum height attained by projectile is momentarily at rest, where the vertical velocity component equals zero.
True or false?
The vertical velocity component of an object in projectile motion at maximum height is zero.
True
What is equation of vertical compent in projectile motion?
Vy= U sin theta
What is equation of horizontal component in projectile motion?
Vx = U Cos theta
what is vertical component of acceleration of an object in projectile motion?
The vertical component of acceleration of projectile is the acceleration due to gravity.
The measurement error that lead to uncertainty is ?
Systematic error.
Random error.
What is the difference between systematic error and random error?
systematic error : measurements may be precise, but not accurate. –> using a stretched measuring tape, scale that always reads to high or low, reading an indicator from a poor angle.
random error : measurements lack precision, but cluster around accurate value. –> timing depends on reaction time, people take turns taking readings, rounding values up or down.
What is zero errors?
Type of systematic error which occurs when an instruments gives a reading when the true reading is zero. For example, the balance starts at 2 g instead of 0 g.
How to reduce reading error?
Use more precise device with smaller measuring intervals and therefore less uncertainty.
What is parallax error?
Occurs due to incorrect positioning of the eyes while taking a reading on a measuring scale. If the viewing angle is not perpendicular to the scale at the point where we are taking the reading, we will get less or more value of the measurement than actual value.
What is the types of uncertainty?
- Degree of uncertainty when measurements are taken
- It not the same as errors : errors can be occur through equipment or methology that cause reading to be different from the true value, while uncertainty is range of values around a measurement within which true value is expected to lie, and is an estimate.
What is absolute uncertainty, fractional uncertainty, and percentage uncertainty?
Absolute uncertainty is given as fixed quantity. absolute uncertainty = 1/2 x 0.2 mA = 0.1 mA –> I = 1.6 +- 1/16mA
Fractional uncertainty is givem as fraction of the measurment.
Percentage uncertainty is given as percentage of the measurent. Percentage uncertainty = (uncertainty/measured value) x 100%
How to find uncertainty in reading, repeated data, and digital readings?
reading: +- half the smallest division
repeated data: +- 1/2 (largest-smallest value)
digital reading: +- the last significant digit unless otherwise quoted.
Note: -Make sure that the number of significant figures is the same as reading.
- Absolute uncertainties (denoted by triangle) have the same units as the quantity.
- The uncertainty is constants, such as (phi), is taken to be zero.
How to do propagating uncertainties / combining uncertainties?
- Adding/subtracting data: add together he absolute uncertainties –> d1= 55.0 +- 0.5 cm & d2= 21.0 +- 0.7 cm –> 55.0-21.0 = 34.0 cm –> +-(0.5+0.7) = +- 1.2 cm –> 34.0 +- 1.2 cm
- Multiplying / dividing data: D= 50.0 +- 0.1 m & T= 5.00 +- 0.05 s –> s=d/t –> s=50.0/5.0=10.0 ms^-1 –> triangle v/v = triangle s/s + triangle t/t –> 0.1/50.0 + 0.05/5.00 = 0.002 + 0.01 = 0.012 –> absolute uncertainty (change of velocity) = 10.0 x 0.012 = +- 0.12 ms^-1 –> v = 10.0 +- 0.012 ms^-1
- Multiply the percentage uncertainty by the power: V = 4/3(phi)r^3 –> r = 2.50 +- 0.02 cm –> V = 4/3(phi)(2.50)^3 = 65.5 cm^3 –> triangle V/V = 3 x triangle r/r = 3 x 0.02/2.50 = 0.024 –> absolute uncertainty (triangle V)+ 65.5 x 0.024 = 1.57 cm^3 – percentage uncertainty (%triangle V)= 100 x 0.024 = 2.4%
How to calculate uncertainty in gradient?
The line of best fit should be drawn on the graph: the ‘best’ line of best fit, which passes as close to the points as possible, the ‘worst’ line of best fit, either the steepest possible or the shallowest possible line which fits within all the error bars.
What is the percentage uncertainty in the graph?
- We can use gradient to find the percentage uncertainty:
Percentage =( (best gradient - worst gradient) / best gradient) x 100% - We can also use the average of two min and max to find percentage uncertainty:
percentage uncertainty = ((max. gradient - min. gradient) / 2) x 100% - We can use the y-intercept to find percentage uncertainty:
percentage uncertainty = ((best y intercept - worst y intercept) / best y intercept) x 100%
percentage uncertainty = ((max. y intercept -min. y intercept) / 2) x 100%
What is percentage difference and how to find percentage difference?
Percentage difference gives indication of how close the experimental value achieved from an experiment is to the accepted value. percentage difference is not the same as percentage uncertainty.
Percentage difference = ((experimental value - accepted value) / accepted value) x 100%
What is experimental value and accepted value?
Experimental value is refer as the measurement value. While accepted value is refered as true value.
Note: The smaller the percentage difference, the more accurate the results of the experiment.
True or False!
Two object side by side must have the same speed.
False, because there is also an object that start from 0 or start more than 0.
True and False!
Acceleration and velocity are always in the same direction.
False, because sometimes acceleration might go to the negative while velocity go to the positive and acceleration might also go to positive but velocity go to negative.
True and False!
If velocity is zero, then acceleration must be zero too.
False. Because when an object is thrown up and experiences free fall, it is constantly accelerating a 10 m/s^2. However, at its highest point, its velocity is zero.
True or False!
Inertia is the force that keeps objects in motion.
False, because inertia is not a force. It is property/characteristic of the object or system determined by the mass distribution.
True and False!
All objects eventually stop moving when a net force is removed.
False, because an object’s inertia (mass distribution) resists any change in motion including a change in velocity.
What is scalar quantities and vector quantities?
Scalar quantities: only have magnitude. For example, distance and speed.
Vector quantities: both have magnitude and direction. For example, velocity, displacement, and acceleration.
Note: In physics, symbol triangle means change.
How do you solving problem with kinematic equations?
Step 1: write out the variables that are given, both known and unknown.
Step 2: choose the equation that contains the quantities you have listed.
Step 3: Convert any units to SI units and the insert the quantities into the equation and rearrange algebraically to determine the answer.
What is independent variable, dependent variable, and control variable in free fall experiment?
- Independent variable is the height
- Dependent variable is time.
- Control variable is same electromagnet, same steel ball-bearing, and distance between ball-bearing and top of the glass tube.
What is the source of error in free fall experiment?
- Systematic error: residue magnetism after the electromagnet is switched off may cause the time to be recorded as longer than it should be.
- Random error: large uncertainty in distance from using a metre rule with a precision of 1mm, parallax error reading h, tha ball may not fall accurately down the centre of each light gate, it can be reduced through repeating the experiment.
What need to be safety considerate in free fall experiment?
- The electromagnetic require to be taken to not have any water near it.
- Switch on the current to the electromagnet once to reduce risk of electrocution.
- A cushion need it to catch the ball, so it doesn’t roll or damage the surface.
- the tall clamp stand need to be attach with G clamp so it stays rigid.
Why in vacuum both feather and apple falls at the same rate?
Because in vacuum, there is no air, which means there is no air resistance. So surface area and mass makes no difference.
Is free fall means that the object is falling down only?
No, free fall is not falling down only. The objects thrown upward or downward and those released from rest are all the example of free fall.
What is mean by acceleration due to gravity?
It means that the ball speed change in each second, the reason of change in speed is due to gravity. Which is why it is called as acceleration due to gravity.
What is projectile motion?
It is the motion of an object thrown (projected) into the air when, after the intial force that lauches the object, air resistance is negligible and the only other force that object experiences is the force of gravity.
Note: The object is called projectile, and its path is called trajectory.
Is projectile motion two-dimensional motion or three-dimensional motion?
It is two-dimensional motion due to the external force and gravity. Projectile motion of any object is parabola.
Two object are released from the same height. Object A fall straight down while object B follows curved parabolic path. Which of them will hit the ground first?
A and B hit the ground at the same time. Because both of them are released from same height. In the absence of any external forces such as air resistance, object will fall towards the ground with the same acceleration due to gravity. Therefore, object will take same amount of time to reach the ground, regardless of their paths or weights.
At what angle to get the greatest range?
45 degree, because it have maximum horizontal distance travelled due to combination of initial velocity and force of gravity. If we choose angle greater than 45 degree, the vertical component of velocity will be increase cause object to spend more time in the air and reducing its horizontal distance.
