1. how does the friction affect forward
motion? give an example.
2. describe two ways to change the
frictional force between two solids surfaces.
change the lubrication between the two surfaces
change the normal force between the two surfaces
3. how does air resistance affect the
velocity of a falling object?
4. what two sources of friction do you
have to overcome when you are walking?
5. if you push a chair across the floor
at a constant velocity, how does the force of friction compare with the force
exert? explain.
6. if you push a book against a wall
hard enough, it will not slide down even though gravity is pulling it. use what
you know about newton’s laws of motion to explain why the book doesn’t fall.

1. what is the relationship between wavelength and the penetrating power of an electromagnetic wave? a) the penetrating power has no relationship to the wavelength. b) the penetrating power increases as the wavelength increases. c) the penetrating power decreases as the wavelength increases. d) the penetrating power decreases as the wavelength decreases. 2. as ice melts and turns into water, the speed of sound through the material would most likely do what? justify your answer. a) the speed would not change because the material is always water. b) the speed of sound would increase because the density of water is less than that of ice. c) the speed of sound would increase because energy is added to ice in order to make it melt. d) the speed of sound would decrease because sound travels faster through solids than liquids. 3.which of these waves need a medium to travel through? a) sound b) x-rays c) infrared rays d) visible light