- these two factors determine the strength of the force of friction friction?
a. speed and light
b. how fast the objects are going and on what planet
c. how big the objects are and how you push them
d. how hard the surfaces pushed together and the types of surfaces involved

- what force is mostly responsible for tides?
a. the gravity of the sun
b. the gravity of the earth
c. the gravity of the moon
d. wind

- which of the following is an effect of friction?
a. when you rub your hands, your pumps feel hot
b. when you rub the matchstick against the side of a matchbox, light and heat or produced
c. you are able to push a cart due to friction
d. all of the above

- what is an example of undesirable effect of friction?
a. producing a fire
b. able to walk
c. wear and tear of shoes
d. able to push a cart

-the steel windows are difficult to close because of some rust on the hingles. what is the best way to loosen them?
a. wash them with detergent and water
b. apply oil or grease on them
c. scrape them with chisel
d. all of the above

-a kindergarten teacher wants to have physical exercises for his/her pupils. what should be applied on floors to prevent injuries?
a. oil
b. water
c. rubber mats
d. grease​