The doctor knows that people taking the medicine may sleep better just because they expect the medicine to work. how can he be sure of whether the medicine really works?

The best test would be doing a double-blind test between the person who is receiving the medicine so that they don't know if they received a placebo or not and the person giving the medicine does not know if the participant is receiving a placebo or not.

However, a placebo test can simply be done. This is where the patient received a medicine that does not have any medicinal effects and see if the person sleeps better. If they say they did, they have fallen under the placebo effect.

d.) circle motion requires a force to give it a centripetal acceleration.

the major pests we deal with are insects, weeds and fungal diseases. a pesticide is a product, whether organic or chemical, used to kill the target pest. there are other techniques gardeners should use that can prevent the severe infestations that make the use of pesticides necessary