Equal gaps, equal times
Telling uniform from non-uniform with a table.
Two trains
Train X and train Y travel on straight tracks between 10:00 AM and 11:00 AM. We note their positions every 10 minutes.
How could the numbers show which train moves at a steady speed?
What this lesson covers
The idea
In uniform linear motion an object covers equal distances in equal intervals of time, and in non-uniform linear motion unequal distances; uniform motion is an idealisation seldom seen in everyday life.
Two trains
Train X and train Y travel on straight tracks between 10:00 AM and 11:00 AM. We note their positions every 10 minutes.
How could the numbers show which train moves at a steady speed?
- Look at the distance covered in each 10 minutes
- Look at the colour of the trains
- Look only at the final stop
Step through the hour
Press Next 10 minutes. Look at the distance covered in each step.
Same or different
Train X covered 20 km in every 10 min. Train Y covered different distances. Same distances in same times mean uniform motion.
In uniform linear motion an object covers equal distances in equal intervals of time, and in non-uniform linear motion unequal distances; uniform motion is an idealisation seldom seen in everyday life.
- Train | Distance in each 10 min | Kind of motion
- X | 20, 20, 20, 20, 20, 20 km | Uniform
- Y | 20, 15, 15, 25, 20, 25 km | Non-uniform
Notes
In uniform linear motion an object covers equal distances in equal intervals of time, and in non-uniform linear motion unequal distances; uniform motion is an idealisation seldom seen in everyday life.
Check yourself
Train X covers 20 km in every 10 min. Its motion is …
Train Y covers 20 km, 15 km, 15 km and then 25 km in successive 10 min. Its motion is …
A car in uniform motion covers 5 km in every 10 min. How many km does it cover in 30 min?
Answer: 15 km
30 min is three intervals of 10 min, and each covers 5 km: 15 km.
Why do we use average speeds in everyday life?
- uniform linear motion — correct. Yes!
- non-uniform linear motion. Equal distances in equal times mean uniform motion.
- not linear. The train moves on a straight track, so it is linear motion.
- uniform linear motion. The distances are not equal, so the motion is not uniform.
- non-uniform linear motion — correct. Yes!
- not possible. Trains can change speed. It is non-uniform linear motion.
- Objects always move at a constant speed. In everyday life, objects seldom move at a constant speed over long distances.
- Average speed is easier to say. The real reason is that uniform motion is an idealisation. Speeds keep changing.
- Objects seldom move at a constant speed for long — correct. Yes!