| How can you:
-Convert from Miles per Hour [mph] to Kilometres per Hour [km/hr]
-Convert from Kilometres per Hour to Meters per Second [m/s] | -Simply Multiply by 1.6, as 1 Mile = 1.6 km. [30 mph = 30 mph x 1.6 = 48 km/h]
-Simply DIVIDE by 3600, from Hours to Seconds - and then MULTIPLY by 1000, from Kilometres to Meters. [OR Divide by 3.6] [48km/h / 3.6 = 13 m/s] |
| What are the Predicted Speeds for
1. Walking
2. Running
3. Cycling
4. Cars in a Built up Area
5, Cars on a Motorway
6. Trains
7. Breeze [Wind Terminology]
8. Gale
9. Sound in Air | 1. 1.4 m/s OR 5km/hr
2. 3 m/s OR 11km/hr
3. 5.5 m/s OR 20 km/hr
4. 13 m/s OR 47 km/hr
5. 31 m/s OR 112 km/hr
6. 55 m/s OR 200 km/hr
7. 5 m/s
8. 20 m/s
9. 340 m/s |
| EXAMPLE:
A Car from rest, Accelerates to 50 km/hr as Fast as Possible
-Predict its Acceleration in m/s | - 50 km/hr = 50 km /hr / 3.6 = 13.88... m/s
-You have to Guess the Time it took for it to reach 13.88 m/s, so pick a Number that is Sensible - 2 Seconds in this Case
-So we use Acceleration = Change in Velocity / Time Taken
-Acceleration = 13.89 m/s / 2 = 7 m/s² [1 Sig Figure] |
| Why can Big Decelerations be Bad? | -A Large Deceleration can be Lethal due to it needing a Large Force, because Force = Mass x Acceleration.
-Also, the Brakes may Overheat as a Result of it, as Lots of Energy is Quickly Transferred to the Thermal Energy Store of the Brakes
-Vehicle may also Skid, which isn't exactly Fun. |
| So what can be done to Prevent a Large Deceleration? | -If you can make the Object Slow down - eg. Slow the Car down over a Long Time, then the Deceleration will be Lower as because
Acceleration = Change in Velocity / Time.
-If the Momentum Changes over a Longer Period, then the Force will be much Smaller as because:
-Force = Change in Momentum / Time |
| Why are their Safety Features in Cars and more? | -It is to Increase the Collision Time, which again Reduces the Deceleration and therefore the Force, which Reduces the Chance for Injury
-Seat Belts will Stretch, Air Bags will slow you Down and Crumple Zones will well Crumple up Easily, making the Time Taken to Increase [Lowers Force and Acceleration]
-Bike Helmets also has a Crushable Layer of Foam, which again Increase the Amount Time Taken for the Head to Stop.
-Shin Pads also Deform when Hit, reducing the Deceleration and Force on your Leg. |
