Do Now 10 Minutes Topic Speed and Velocity Clear off everything from your desk, except for a calculator and something to write with. We re taking a pop quiz.
Homework Complete the Distance vs. Displacement Lab Report Test Correction Pages Work is to be done on a separate piece of paper AND submitted with the test corrections sheets. NOTE: ALL PERIOD 4 HOMEWORK WILL BE DUE ON B-DAYS Due 10/10/14
Homework Hypothesis Assignment Significant Figures Worksheet Measurement vs Accuracy Lab Interim Reports are being sent out Friday. If you want these grades in there, get these assignments to me by TOMORROW.
Test Correction Page Number: Which question are you correcting? Type of Question: Dimensional Analysis, Scientific Notation, Significant Figures, etc. Question: Rewrite the question that you are correcting Answer: What is the CORRECT answer to the question? Reason Why: Explain why you got the problem wrong.
Additional Reading Many of the topics we are going to cover now are actually in the textbook. You do not have textbooks to take home, so I will scan in the pages after school and upload them to the class website. I will post when it s up on the class Twitter.
Speed A lot of Physics involves objects in motion. To begin to understand moving things, we need to talk get some terminology out of the way. It is not helpful to say something is fast, or even slow. Fast is a relative term.
Relative Speeds When we say fast, do we mean fast like a runner? (6 m/s) (13.4 mph) Or fast like Usain Bolt? (10.44 m/s) (23.35 mph)
Relative Speeds Fast like Lance Armstrong? (15 m/s) (34 mph) Or fast like Michael Schumacher? (103 m/s) (230 mph)
Relative Speeds Fast like a Boeing 747? (250 m/s) (514 mph) (2 hrs, 32 min from Newark to Miami) Or fast like a SR-71 Blackbird? (958 m/s) (2,143 mph) (That would be flying from Newark to Miami, FL in 30 minutes!)
Relative Speeds Fast like the Earth? (30,000 m/s) (67,108 mph) Or fast like the speed of light? (300,000,000 m/s) (671,080,887 mph)
Speed In all of these cases (except for the speed of the Earth), what is our reference point? The surface of the Earth, or an unchanging point. If we want to discuss how quickly (or slowly) an object moves, then we can talk about an object s speed. Speed is how fast an object is moving.
Speed Speed is equal to distance traveled divided by time. Speed= Distance Time Based on what you know about the SI system, what should the units for speed be? The units for speed and velocity are meters / second or m/s.
Sample Problem Roland rides his bike 300 meters in 50 seconds. What is his speed during this ride? Speed= = = 6 m/s
Distance Looking at our formula for speed, is it possible we can determine the distance an object travels? Speed=. Multiply both sides by time Distance [m] = Speed [m/s] x Time [s]
Distance Sample problem: In 2013, Tony Kanaan s average speed at the Indy 500 was 301 km/hr. If the race was 2.65 hours long, what distance did he travel? Identify what pieces of information we have. What formula should we use? Distance [m] = Speed [m/s] x Time [s] Distance = 301 km/hr x 2.65 hr = 797.65 km
Which Speed? Whether it s a car, person, or bike, do objects always travel at the same speed? If we want to know an objects speed at any given instant, we look at its instantaneous speed. Instantaneous speed: an objects speed at any given instant. How you would a car s instantaneous speed.
Instantaneous Speed A car s speedometer tells us its instantaneous speed. A radar gun can also determine a car s instantaneous speed.
Which Speed? Were we using instantaneous speed when we calculated the cyclist s speed in the beginning of class? Were we using instantaneous speed when we calculated what distance Tony Kanaan travelled? No to both. We were using average speed.
Average Speed Average speed is the total distance travelled divided by total time. Average speed does not indicate variations in speed during a trip (red lights, speeding, etc.). The formula you write down in the beginning of class was your average speed. We ll be learning a formula for instantaneous speed after we learn about acceleration.
Examples Mr. Fineman lives 5800 m (3.4 miles) from VHS. It takes him about 15 minutes to get to school. Convert Mr. Fineman s travel time to seconds. 900 seconds Calculate Mr. Fineman s speed when he drives to school. 6.4 m/s (14.3 miles/hour) Justify: Is Mr. Fineman truly going 6.4 m/s the entire ride here? Why or why not.
Speed vs Velocity So far we have just talked about speed. However, in the English language, we tend to use the words velocity and speed interchangeably. Speed is how fast you re going. Velocity is speed in a given direction. Speed is a SCALAR Velocity is a VECTOR.
Velocity Example: If we say you run 5 m/s we are talking only about speed. If we say you run 5 m/s to the West, we are talking about velocity. Speed is a description of how fast an object moves; velocity is how fast and in what direction it moves.
Relatively Easy Problems A train passes you travelling at 20 m/s to the right. You are not moving. 0 m/s 20 m/s Relative to you, how fast is the train moving? (20 m/s 0 m/s) 20 m/s to the right!
Relatively Easy Problems A train passes you travelling at 20 m/s to the right. As the train is leaving, you start sprinting after it at a rate of 3 m/s to the right. 3 m/s 20 m/s Does the train seems to be moving away from you faster or slower than before. Relative to you, how fast is the train moving? (20 m/s 3 m/s) = 17 m/s
Relatively Easy Problems A train passes you travelling at 20 m/s to the right. As the train is leaving, you hop in a car and drive away 10 m/s to the left. 10 m/s 20 m/s Does the train seems to be moving away from you faster or slower than before. Relative to you, how fast is the train moving? (20 m/s + 10 m/s) = 30 m/s