8th Science - Chapter 5 Review

   1.  Friction

   2.  newton

   3.  net force

   4.  velocity

   5.  weight

   6.  B

   7.  D

   8.  C

   9.  C

10.  C

11.  Motion occurs when an object changes position over time when ­compared with a reference point (an object that appears to stay in place).

12. Acceleration can occur simply by a change in direction. Thus, no change in speed is necessary for acceleration.

13.  Mass is the amount of matter in an object, and its value does not change with the object’s location. Weight measures the gravitational force on an object, so it can change as the amount of gravitational force changes.

14.  a. 12 m/s

b. 12 m/s east

c. 2.5 m/s² south

15.  

16.  Sample answers: Use a handcart or dolly to take advantage of rolling kinetic friction. Polish the floor to reduce sliding kinetic friction.

17.  The car’s gas pedal is pressed by the driver to increase the car’s speed. Since the scientific meaning of the term acceleration can include slowing down and even changing direction, accelerator is not an accurate term for this device.

18.  It is helpful for pilots to know wind velocity because velocity includes direction. Pilots need to know the wind’s speed and direction so that they will know whether the wind is blowing in the same direction as the plane (which could increase the plane’s resultant velocity and lead to an earlier arrival time) or in a different direction than the plane (which might lead to a later arrival).

19.  The graph shows positive acceleration. Velocity increases as time passes.

20.   a. 3 N to the left

b. 5 N up

c. 8 N to the right