3.4 Time, Distance and Speed

• Speed in km/h and m/s
• Average speed
• Acceleration
• Longitudes and local time

• work out speed in km/h and m/s in real-life situations
• work out average speed in real-life situations
• determine velocity in real-life situations
• work out acceleration in real-life situations
• identify the longitudes on the globe
• relate longitudes to time on the globe
• determine the local time of places on the earth along different longitudes
• appreciate the use of time and distance in real-life situations

“How do we observe speed in daily activities?”

“Why does time vary in different places of the world?”

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1. Speed: distance divided by time
   40 min · 1 practice tasks · quiz
   Speed is not measured directly. It is what a distance becomes when you divide it by the time it took.
2. Speed in km/h and in m/s
   40 min · 1 practice tasks · quiz
   One number, 3.6, converts a speed either way between kilometres per hour and metres per second.
3. Finding the distance or the time
   40 min · 1 practice tasks · quiz
   The same relationship rearranges to give distance from speed and time, or time from distance and speed.
4. Average speed
   40 min · 1 practice tasks · quiz
   Add all the distance, add all the time, then divide once. Never average the leg speeds.
5. Velocity: speed with a direction
   40 min · 1 practice tasks · quiz
   Two vehicles can share a speed and still have different velocities, because velocity carries a direction.
6. Acceleration
   40 min · 1 practice tasks · quiz
   Acceleration is the change of velocity in each second, and a negative answer means slowing down.
7. Measuring speed at a track event
   40 min · 1 practice tasks · quiz
   Take the class outside and measure distance, time, speed and acceleration on a real run.
8. Longitudes on the globe
   40 min · 1 practice tasks · quiz
   Meridians run from pole to pole, and Greenwich is the zero from which the rest are counted east and west.
9. Fifteen degrees to the hour
   40 min · 1 practice tasks · quiz
   The earth turns 360 degrees in 24 hours, so each 15 degrees of longitude is one hour of time.
10. Working out the local time of a place
    40 min · 1 practice tasks · quiz
    Find the longitude difference, divide by 15, then add going east or subtract going west.