Introduction to Physics. What is Physics?. Physics is the study of how things work in terms of matter and energy at the most basic level. Physics is everywhere! Some areas of physics include: Thermodynamics Mechanics Vibrations and wave phenomena Optics Electromagnetism Relativity
Physics is the study of how things work in terms of matter and energy
at the most basic level.
Physics is everywhere!
Some areas of physics include:
Vibrations and wave phenomena
Physicists use models to help build hypotheses , guide experimental design and help make predictions in new situations .
Sometimes the experiments don’t support the hypothesis. In this case the experiment is repeated over and over to be sure the results aren’t in error. If the unexpected results are confirmed, then hypothesis must be revised or abandoned. As a result the conclusion is very important. A conclusion is only valid if it can be verified by other people.
Keep in mind in that any theory, no matter how firmly it becomes entrenched within the scientific community, has limitations and at any point may be improved.
ie. There is always a possibility that a new or better explanation can come along.
In physics there is an organized approach that breaks down the task of obtaining information to solve a problem.
Often, the more problems you work on the better you get at solving them.
Physics usually involves the measurement of quantities.
In Physics, numerical measurements are different from numbers used in math class.
In math, a number like 7 can stand alone and be used in equations.
In science, measurements are more than just a number.
For example, if you were to measure your desk and report the measurement to be 150.
This leads to several questions:
Other units are found by combining these fundamental units:
To convert between units we need to multiply by a factor of one.
1Mm = 1 and 106 m = 1
106 m 1Mm
652Mm x 106 m
=652 x 106 m
=6.52 x 108 m
What is 200 km/h in m/s?
* don’t forget that if you are adding two measurements, they must have the same units.
Accuracy is how close the measured value is to the true or accepted value.
For example, when you read the volume of a liquid you will get a different measurement if you look at the meniscus from different angles. This phenomenon is called parallax
Problems with accuracy are due to error. Experimental work is never free of error but it needs to be minimized.
Instrument error can also occur. This occurs when a device is not in good working order. When lab equipment isn’t handled properly problems with accuracy arise.
Ex. Balances damaged, tare, wooden meter stick got wet etc…
When we are taking a measurement the last digit that we measure is estimated to a degree. In this course we will assume that you can make a fair estimate to about ½ of the smallest increment.
Because of the uncertainty in the last digit of your measuring device, we indicate that we are estimating our value to within ± ½ of the smallest increment.
When you are taking measurements, the percent error is also important. To find the percent error in your measurements:
|accepted value – measured value| x 100%
On the other hand, the zero in ".03" is not a significant figure. It is important though, because if we leave it out and write .3 then the value is completely different from .03 (it is 10 times bigger). Thus, such zeroes are said to "place the decimal", and not considered "significant".
Sometimes .03 is written as 0.03. The first zero also does not change the value of the number, but neither does it indicate more precision. It is generally included to stress the location of the decimal point, and its inclusion is never essential.
All digits are significant with the exception that:
1. leading zeroes are NOT significant (0.0005 has only one sig. fig.)
2. tailing zeroes in numbers withoutdecimal pointsare ambiguous. (zeroes in 700 are not, but the zeroes in 700.0 are)
5200 as stated is assumed to have 2 sig. fig.
If it were to have 3 sig. fig., it should have been expressed as 5.20 x 10 3.
If it were to have 4 sig. fig., it should have been expressed as 5.200 x 103,
30 is assumed to have one sig.fig. If you have to report such a number, you MUST express it in scientific notation.
conversion numbers are always
When adding and subtracting with significant figures, the answer should have the same number of digits to the right of the decimal as the measurement with the smallest number of digits to the right of the decimal.
round off to 103.2
When multiplying or dividing the final answer must have the same number of significant figures as the measurement having the smallest number of significant figures.
658.05 round off to 658
When adding or subtracting AND multiplying or dividing, you must keep track of your significant figures but save your rounding until the end.
(10.2 + 2.45) x 6.9
=12.65 x 6.9
(4.2 – 4.18) x 19
= .02 x 19
(32.01 + 12.2) x 623
=(.02 +.612) x 3.12
=(.02 + .3721) x 3.12
=(.3921) x 3.12
The best way to represent a set of data is by drawing a graph. We need to determine which variables are the independent variables and the dependent variables.
Dependent variables are the ones that respond to the manipulation (y axis)
A car drives at a certain speed, brakes and travels a certain distance before it comes to a full stop.
distance and time
Independent: time Dependent: distance
Distance vs Time
** do not do dot to dot**
Scaling your Axes: On your graph paper you have a set number of division s for each axis. You proceed as follows to assign the value for each division:
Division value = largest data - smallest data
Number of divisions
For time (x axis) we have _____ divisions and a range of 0s to 7.0s
div. value = = s/div
You have some leeway to round this value up to a convenient value, say, __________ s/div, but you cannot round it down (your data will not fit on the graph if you do). This method allows us to use the maximum spread of the graph paper, giving us a longer line and more accurate slope calculations.
Curved lines: Use your elbow as a pivot and ghost your pencil over the points, fine tuning your curve with your hand.
The dependent variable varies linearly with the independent variable in the form
y = mx + b
b = y intercept or where the line crosses the y
m = rise = Δy = yf - yi
run Δxxf - xi
Smooth line curves upwards in the form
y = kx2
where k = some constant
Smooth line curves downwards in the form:
y = k ( ) = kx-1
Time is an important measure of events in physics.
There are two quantities that we can record that will give us a sense of time.
Frequency is the number of events that occur within a given amount of time (usually represented by f )
The number of times a guitar string vibrates back and forth might be 300 times /second or 300 s-1. We measure frequency in Hertz [Hz]. So, instead we would say that the guitar string has a frequency of 300Hz.
Period is the time it takes for an event to complete one cycle (usually represented by T).
Example: The time it takes for one complete vibration of the string would be 1/300th of a second or
As you can see, period and frequency are inversely related so:
Period = 1 or T = 1
Objective: (or Purpose): In your words, not just copied
from the lab handout.
Materials: Rewritten from lab handout. Add or delete items
Procedure: “As on lab handout”. Then note any changes
Data should be in a table with lines and appropriate units. Make sure all data is taken with the same precision.
*don’t forget your uncertainty
Observations must be in full sentences.
Should be on one WHOLE sheet of graph paper
Should have the correct units
Line of best fit (for linear data)
Correct labeling of data points
USE A RULER
All questions should be answered in full sentences.
Always give your reasoning or an explanation.
Conclusion: Give 3 or 4 full sentences that respond to the objective of the lab and summarize your work. You should include 2 or 3 sources of error.
Staple all rough work, especially your original data collection to your lab
YOUR LAB SHOULD BE NEAT.
NEAT I SAY!
Galileo’s thought experiment on objects
at the same speed:
Two objects fall at the same speed. If you tie them together (doubling the mass) they should fall at a faster speed.
His theories were used to predict the motion of many things in free fall such as raindrops or boulders.