Lesson 4 — More indepth on calculating speed

• Natuurkunde / Scheikunde
• Middelbare school
• havo
• Leerjaar 1

This lesson

• Recap
• Discussing the homework
• Average speed & steady speed.
• Converting km/h <-> m/s
  

Goals

• You Know how to rearrange the formula for speed
• You are able to explain the difference between steady and average speed
• You are able to calculate average speed
• You Know how to convert km/h <-> m/s

Recap

Speed

Speed=​time​​Distance​​

v=​t​​d​​

New physical quantity:

Speed

Unit of Speed:

• m/s
• Km/h

Formula

• v: speed (meters/second) m/s)
  
• d: distance (meters) (m)
• t: time (seconds) (s)

The amount of distance something is traveling over a certain time.

Examples:

• A runner is running at a speed of 3/ms
• A car on the highway is driving at a speed of 120 km/h

Discussing the homework

Rearranging the formula for speed

Rearranging the formula for speed

v=​t​​d​​

3=​2​​6​​

Rearranging the formula for speed

v=​t​​d​​

Speed: 

Distance:

Time:

Rearranging the formula for speed

v=​t​​d​​

Speed: 

Distance:

d=v⋅t

Time:

Rearranging the formula for speed

v=​t​​d​​

Speed: 

Distance:

d=v⋅t

Time:

t=​v​​d​​

Discussing the homework

Average speed & steady speed

Speed:

How fast something is moving

Average speed

total distance divided

by total time

Steady speed

Traveling at a constant speed

Average speed

avaragespeed=​totaltime​​totaldistance​​

Exercise

You are an engineer at a formula one race track. One practice track has three parts to it. Part one with a length of 22,3 km. Part two with a length of 33,5 km. and part three with a length of 17,9 km. A race car speeds through this track two times. The first time it complets it in 19 minutes and 40.8 seconds the second time in 18 minutes and 27 seconds. 

Calculate the average speed of this formula one race car.

avaragespeed=​totaltime​​totaldistance​​

Converting 

km/h <-> m/s 

Exercise

• A car travels 72km/h. What is that in m/s?
  
• A cyclist travels 7 m/s. What is that in km/h?

Exercise

• A car travels 72km/h. What is that in m/s?

• In one hour the car travels 72km = 72000 m
• One hour = 3600 seconds
• So in 3600 seconds it travels 72000 m
• Then in 1 second it travels 72000/3600 = 20 m/s
• So a speed of 72km/h converts to 20 m/s

Exercise

• A cyclist travels 7 m/s. What is that in km/h?

The cyclist travels 7 meters in one second

There are 3600 seconds in one hour

So in one hour the cyclist travels 7m x 3600 = 25200m

25200m = 25.2 km. the cyclist travels 25.2 km in on hour.

So a speed of 7 m/s converts to 25km/h.

km/h —> m/s

The speed x 1000/3600

m/s —> km/h

The speed x 3600/1000

Exercise

Convert a speed of 38 km/h to m/s

Convert a speed of 1.5 m/s to km/h

km/h —> m/s

The speed x 1000/3600

m/s —> km/h

The speed x 3600/1000

Exercise

Convert a speed of 38 km/h to m/s      =      10.55 m/s

Convert a speed of 1.5 m/s to km/h      =      5.4 km/h

km/h —> m/s

The speed x 1000/3600

m/s —> km/h

The speed x 3600/1000

Homework

Do: 4.1 Workbook exercises

Goals

• You Know how to rearrange the formula for speed
• You are able to explain the difference between steady and average speed
• You are able to calculate average speed
• You Know how to convert km/h <-> m/s