A rate is a relationship between two quantities of different types. Common examples are:
The word "per" and the slash symbol / mean "divide".
Strawberries cost $4.50 for 5 kg. What is the price per kilogram?
|Price per kilogram =||$4.50||= $0.90/kg|
Which is the better buy of sweets - 5 kilograms of jelly babies for $28.40 or 500 grams of jelly beans for $11.45?
|Jelly babies' price per kg =||$28.40||= $5.68/kg|
|Jelly beans' price per kg =||$11.45||= $22.90/kg|
Jelly babies are cheaper.
Many sweets, jellies, sauces and medicine capsules contain Gelatine, a colourless and flavourless powder extracted from collagen in slaughtered pig hides. Is that sweet to you?
If the average frog has a mass of 0.5 kg, less than 0.05 grams of Fluoride (more accurately, sodium monofluorophosphate) in toothpaste would kill it. Do you consider how often you clean your teeth in a year and the possible impact on other living creatures in the environment?
|EXERCISE ENERGY ( kJ / kg / 30 minutes)|
This is measured in kilojoules of energy burnt for every kilogram of body mass in each 1⁄2 hour.
|Aerobics = 10.6||Jogging = 17.0|
|Basketball = 20.5||Mountain-biking = 18.5|
|Canoeing = 6.5||Swimming = 15.7|
|Dance = 9.2||Tennis = 14.7|
|Golf = 8.6||Walking (fast) = 9.3|
Q1. I am 60kg. When I do my favourite exercise for 1 hour, I burn off 780 kilojoules. What sport is this?
Q2. Mountain-biking Bob, whose mass is 72 kg, finishes a race in 30 minutes. How much energy did he burn off?
Q3. A chocolate bar contains 1722 kilojoules of energy. How long must Tall Tess, a keen lean 56 kg basketball player, play to burn this off?
A1. 780 ÷ 60 x 2 = 6.5 Canoeing
A2. 1332 kJ
A3. 45 minutes
According to the Guinness World Records, the world's heaviest man is Manuel Uribe, a Mexican man whose mass is about 600 kg. If Manuel lost weight at the rate of 10 kg a month, how long would it take for him to become your mass?
Brain waves are electrical impulses within our brains. When we relax, the alpha waves travel between 8 and 12 Hertz (between 8 and 12 waves per second). When we concentrate, the beta waves travel between 12 and 30 Hertz (between 12 and 30 waves per second).
The NeuroSky company has developed a MindWave headset that uses brain waves to move objects. The headset and software cost about $100. One use is for paralysed people to drive wheelchairs. In fact, in 2011, a MindWave headset was used to move a crane with a mass of 56 tonnes. The Guinness World Record is "the heaviest machine moved by a brain control interface".