A scientist is testing how caffeine affects people’s sleep. She asks one group of people to drink one can of Coke before bed. She asks a second group of people to drink one cup of water before bed. Over a period of one month, she determines that the Coca Cola drinkers slept 45 minutes less per night than the water drinkers. What is the INDEPENDENT VARIABLE?

The type of drink with different caffeine contents.

Explanation:

When conducting an experiment, two variables are looked out for, they are: independent variable and dependent variable. Independent variable refers to the variable being controlled or altered in the experiment in order to induce an effect in the dependent variable, which is the variable being measured. The outcome of the dependent variable is dependent on the input or independent variable.

In this question, the scientist is testing how caffeine affects people's sleep. She uses different drinks i.e. Coca-Cola and water with different caffeine contents to test out it's effect on the time of sleep people in the different groups will have. Therefore, the type of drink is the INDEPENDENT variable because it is being changed to test an effect on the dependent variable. The amount of time of sleep is what is being measured, hence it is the dependent variable.

before, trains worked using the steam engine. thus, it uses heat so it is crucial to apply heat balance. the steam engine absorbs energy during the stage of boiling water. so, this is the endothermic reaction. when the steam is used to work the piston, it has to release this energy through running the train. the excess energy is released as an exhaust to the chimney. this is the exothermic process because it releases energy to the surroundings.