Physics Ch. 1+2 Review
Quadratic relationship
(Parabolic), one variable depends on the square of another. Y= ax^2+bx+c
Motion diagram
(Running diagram) a series of images showing the positions of a moving object at equal time intervals
Convert each of the following: 42.3 cm to meters 21 km to meters 260 mg to grams 18.87 kg to grams 86,400 seconds to days 30 km/h to m/s
42.3 cm is .432 m 21 km is 21,000 m 260 mg is .260 g 18.87 kg is 18,870 g 86,400 seconds is 1 day 30 km/h is 8.3 m/s. Convert 1 thing at a time: 30 km/h is 30,000 m/h. 30,000 m/h is 500 m/min (we divided by 60 min/h), and 500 m/min is 8.3 m/s (we divided by 60 s/min)
The temperature in Mrs. McLain's class drops from 24C to 10C in 12 hours. 1. Find the average temperature change per hour. 2. Predict the temperature in 2 more hours if the trend continues.
8a: 1.2 C/h (24-10 = 14 degrees over 12 hours. 14/12 = 1.2) 8b: If you know it's going down by 1.2 degrees each hour, then it would be 2.4 degrees colder after two hours. Since it's 10 degrees now, it would drop to 7.6 degrees C
During a class demonstration, your physics instructor places a mass on a horizontal table. The instructor then applies various horizontal forces to the mass and measures the distance it travels in 5 seconds for each force applied. The results are given by following: 5N force = 24 cm 10N force = 49 cm 15N force = 75 cm 20N force = 99 cm 25N force = 120 cm 30N force = 145 cm 1. Plot the values given in a table, draw a scatter plot and draw a best fit line for your data points. 2. Describe the resulting curve as linear, quadratic or inverse. 3. Use the graph to write an equation relating the distance to the force. 4. Predict the distance traveled when a 22N force is exerted on the object for 5 seconds.
9.1: Your graph should have Force on the X-axis and Distance on the y-axis. Ideal increments would be about 10.0N of Force and 40 cm respectively, but you can make your increments whatever makes sense to you. 9.2: The resulting curve is a straight line. 9.3: F = 4.9 d 9.4: If a constant force of 22N is exerted on this object, we know it would travel about (22 N * 4.9 cm/N) about 108 cm, regardless of how long it's pushed. Our graph only relates Force and distance.
Position-time graph
A graph represented by plotting time on the horizontal (x) axis, and the position on the vertical (y) axis. North, south, east, or west would be at the ends of the y axis
What is the purpose of drawing a motion diagram
A motion diagram gives you a picture of motion that helps you visualize displacement and velocity.
Derived Unit
A product of one or more of the 7 base units
Vector
A quantity that has both size (magnitude) and direction, can be represented by arrows
Scalar
A quantity that is just a number without any direction (ex: distance, time, temperature)
Linear relationship
A type of relationship that exists between two variables whose graphed data points lie on a straight line. Y=mx+b. Y-dependent, x-independent, b-y-intercept, m-slope. Graph not a straight line- relationship between independent and dependent variable is not linear
Accuracy
Agreement with the "real" value
Physics
Branch of science that involves the study of the physical world: energy, matter and how they are related
SI Unit
Created to define and regulate measures using the metric system
Particle model
Draw with dots representing object (a motion diagram but with dots instead of images)
Dependent variable
Factor that depends on the independent variable
Independent variable
Factor that is changed or manipulated during the experiment, the difference
Nico is driving down Basswood at 55 km/h. Logan suddenly runs into the street (silly Logan)! If it takes Nico 0.75 s to react and apply his brakes, how many meters will his car have moved before it begins to slow down?
First let's convert Nico's 55 km/h into m/s. We don't have to, but it will make a lot more sense that way since the other option is to convert his 0.75s reaction time into hours! (A very small number!) So: 55 km/h * 1000 m/km / 3600s/h = 15.3 m/s. Now: d = vt. We have v, 15.3 and we have t, 0.75. Plug that in: d = (15.3 m/s)(0.75) = 11 m
Scientific notation of different units (prefix chart)
Giga- 10^9, Mega- 10^6, Kilo- 10^3, Base (g, m, etc)- 10^0, deci- 10^-1, centi- 10^-2, milli- 10^-3, micro- 10^-6, nano- 10^-9
Distance
How far the object is from the origin
Why do we use the SI system of measurement?
It uses units that everyone understands and it is easier to switch between its units
Light from the Sun reaches Earth in 8.3 min. The speed of light is 3.00 x 10^8 m/s. How far is the Earth from the Sun?
Let's make our units match up first. You can't do math with minutes and seconds at the same time! (Pun intended.) 8.3 minutes * 60 s/min is 498 seconds. d = vt. We have v and t now so: d = (3.00 * 10^8 m/s)(498 s) = 1.5 * 10^11 meters. (That's about 93 million miles!)
Best fit line
Line drawn as close to all the data points as possible. It is a better model for predictions than any one point that helps determine the line
Scientific method
Make predictions- make observations- obtain data- do experiments- find results
To convert 1.8h into minutes, by what should you multiply? Why?
Multiply by 60 since there are 60 minutes per hour
Significant digits
Non-zero digits, final zeros after a decimal point , zeros between two significant digits, zeroes used only as placeholders are not significant. Start counting from front if decimal, from back if not. Ex: 5.0=2, 14.90=4, 0.00420=3, 5700=2
Inverse relationship
One variable depends on the inverse of another, results in a hyperbola, y=a/x
Model
Results of an experiment in physics lead to an idea, equation, structure, or system that can model a phenomenon. If new data doesn't fit the model, the data and the model are re-examined
How do you find the slope of a linear graph?
Rise over run
When adding or subtracting significant digits
Round the answer to the least number of decimal places. Ex: 1.457+ 83.2= 84.657-> 84.7
When multiplying or dividing significant digits
Round the answer to the least number of significant digits. Ex: 4.36 x 0.00013= 0.0005668-> 0.00057
Magnitude
Size
Average velocity and average speed
Speed + direction, distance/time. V= Δd/Δt = df-di / tf-ti (slope of a position time graph)
Coordinate system
Tells the location of the zero point of the variable you are studying and the direction in which the values of the variable increase
Your car's odometer measures the distance from home to school as 3.9 km. Using some string on a map, you measure the distance to be 4.2 km. Which answer do you think is more accurate? Justify your answer
The car is probably more accurate since you drove the actual, real-life distance, whereas a map is an approximation
Displacement
The change in position during the time interval between ti and tf. The length of the arrow represents the distance moved. The direction of the arrow indicates displacement. Δd= df- di
Precision
The degree of exactness, significant digits show precision
Time interval
The difference between the initial and the final times. Time interval= Δt (Δ represents a change in a quantity). Δt= t(subscript f) -tᵢ
Independent and dependent example
The following research questions was posed: Do people who live in a city walk more and weigh less than similar individuals in a suburb? Determine which quantity is the independent variable and which is the dependent variable.— Whether someone lives in a city or a suburb-independent; Distance walked and Weight-dependent
Origin
The point at which both variables have the value zero
Position
The separation between an object and the origin. Exactly where an object is located (left or right AND the distance), can be negative
The density of a substance is its mass per unit volume. Give a possible metric unit for density. Would this be a base unit or a derived unit?
The unit for density is kg/L. Since it's a combination of two base units, it's a derived unit
Resultant
The vector that represents the sum of two or more other vectors, always points from the tail of the first vector to the tip of the last vector
Test rules
V= 5m/s don't forget the V (what you're solving for), draw arrow on vector, position (m), time (s or hr), units and direction
What does the slope of a position-time graph measure?
Velocity
Julia and Peyton are each taking their cars to the lake which is 50km away from HCA. Draw a position-time graph based on the following information: Julia is leaving at noon from her house which is actually 10km closer to the lake than the school, and drives at 40 km/h. Peyton leaves from school during lunch at 12:30 but is moving at 100 km/h. Using this information, at what time does each car get to the lake?
Your P/T graph should have time in the X-axis and Position (in kilometers, since your distances in the problem are all given in kilometers) for the Y-axis. Since Julia's house is 10km closer, it should start its line at the 10 position of your graph (b=10). Since Peyton leaves at 12:30, her line shouldn't start until the 12:30 time on your graph (b=0). Julia's slope should be much less than Peyton's since her velocity is less. Plotted correctly, the lines representing their velocities should intersect at the 50km point, meaning that they arrive at the same time!
Measurement
a comparison between an unknown quantity and a standard. Measurements quantify observations
Scientific law
a rule of nature that sums up related observations to describe a pattern in nature
Scientific theory
an explanation based on many observations supported by experimental results
Jordyn and Hillary each drive 50.0 km. Jordyn travels at 90.0 km/h, but Hillary travels at 95.0 km/h. How long will Jordyn have to wait for Hillary at the end of the trip?
d = vt, or t = d/v. You want t in this case since the question is asking for a time. Now let's get Jordyn's time first: t = 50 km / 90 km/h = 0.556 h. Hillary's time would be: t = 50 / 95 = 0.526 h, a difference of 0.03 hours. Since there's 60 minutes in an hour, multiply 60 by 0.30 to get 1.8 minutes. So Jordyn will wait for Hillary for 1.8 minutes (or 1 minute and 48 seconds).
Skyler is riding a bike at a constant speed of 4.0 m/s for 5.0s. How far does he go?
d = vt; So, d = (4.0 m/s)(5 s) = 20m
