Introduction to Physics & Measurement
“Physics is only about things moving.” Is this statement correct?
No. Physics studies matter, energy, motion, forces, interactions, and many other physical phenomena.
A student walks from their desk to the door. Is the student in motion? What must change for us to say that the student is moving?
Yes. Their position must change relative to a reference point.
Two runners both finish a 100 m race. Runner A takes 10 s and Runner B takes 12 s. Who has the greater average speed?
Runner A, because they cover the same distance in less time.
Convert 4.25 km to meters.
4,250 m
A dog runs 80 m in 10 s. What is its average speed?
8 m/s
Imagine that you need to measure the length of a table, but you don’t have a ruler. You decide to use pencils. Why might two students get different results if they use different pencils?
Because the pencils may have different lengths. A standard unit gives everyone the same reference.
You are sitting inside a moving bus. Are you at rest or in motion? Explain why both answers can be correct.
You are at rest relative to the bus, but in motion relative to the road/buildings. Motion depends on the reference frame.
A cyclist travels 240 m in 30 seconds. What is their average speed?
8 m/s
A movie lasts 2.5 hours. How many seconds is that?
9,000 s
A cyclist travels 500 m east and then 200 m west in a total of 70 seconds. What are the distance and displacement?
Distance = 700 m; displacement = 300 m east.
Why is it more useful for scientists in Mexico and Japan to use the same measurement system instead of creating their own units?
It allows scientists to communicate, compare, and reproduce measurements consistently.
Maria walks 8 m east from her house and then 3 m west. What is her total distance and what is her displacement?
Distance = 11 m. Displacement = 5 m east.
A car travels at 20 m/s. How far will it travel in 15 seconds?
300 m
A runner’s speed is 72 km/h. Convert it to m/s.
20 m/s
A car travels 2 km in 2 minutes. What is its average speed in m/s?
16.67 m/s
A kilometer, meter, and centimeter are all SI base units. Is it true? Explain.
No. The meter (m) is the SI base unit for length. Kilometer and centimeter are metric units derived from the meter using prefixes.
A runner completes one 400 m lap around a track and finishes exactly where they started. What are the runner’s distance and displacement?
Distance = 400 m. Displacement = 0 m.
A student runs 150 m in 20 s. What is their average speed in km/h?
7.5 m/s = 27 km/h
A car travels at 15 m/s. Express its speed in km/h.
54 km/h
Sofia walks 100 m north in 40 s, then 60 m south in 20 s. Calculate: A) total distance, B) displacement, C) average speed.
A) 160 m; B) 40 m north; C) 2.67 m/s.
A scientist measures the length of a microorganism as 0.000005 m. Why would using a smaller unit such as micrometers be more convenient? Convert the measurement to micrometers.
Smaller units make very small measurements easier to express. 0.000005 m = 5 μm.
A student walks 12 m north, then 7 m south, and finally 5 m north. What are the student’s total distance and displacement?
Distance = 24 m. Displacement = 10 m north.
A car travels 100 m east in 10 s, then 60 m west in 5 s. What are its total distance, displacement, and average speed?
Distance = 160 m; displacement = 40 m east; average speed = 10.67 m/s.
A spaceship travels 450,000 km in 15 hours. What is its average speed in km/h and m/s?
30,000 km/h = 8,333.3 m/s
Carlos forgot his phone in the cafeteria. The cafeteria is 95 m away. He has only 6 minutes before the class starts. What minimum average speed does he need in m/s and km/h to reach the cafeteria?
95 ÷ 360 = 0.264 m/s = 0.95 km/h.