Download 2.1 Observe and Analyze The diagrams are not consistent. The ball

Sierzega: Dynamics 2 Solutions
2.1 Observe and Analyze
Observer
You on a train that is
starting to move
Your friend on the platform
Motion diagram for the ball
(description of motion)
Δv = 0
Δv
Force diagram for the ball
(explanation of motion)
Are the diagrams consistent?
Explain.
F table on ball
F table on ball
F Earth on ball
F Earth on ball
The diagrams are not
consistent. The ball changes
its velocity to the right
without a net force exerted
on it by other objects.
The diagrams are consistent.
There is no change in motion
and no net force exerted on the
ball by other objects.
c) There is no unbalanced force exerted on the ball, and yet the ball moves towards the right
according to the observer on the train.
d) The direction of the change in motion is in the same direction as the net force exerted on
the object for non-accelerating observers.
e) My friend did not see the ball move because relative to her, the ball did not move. The
train moved around the ball. The ball’s motion was independent from the train’s.
2.2 Explain
a) A bowling ball rolls down an alley at a constant speed. A book is at rest on a table.
b) The person who is standing still in the bowling alley will see the bowling ball rolling
down the alley at a constant speed. A person walking away from the book on the table at
a constant speed will see the book moving away from them at a constant speed.
c) Any object that is accelerating with respect to the object of interest (bowling ball or
book) will see this object as accelerating.
d) The picture should indicate that the observer in question b sees the object as moving at a
constant speed while the observer in question c sees the object accelerating. Remember
the idea of motion is relative so whether or not the observer is changing his or her motion
determines whether other objects perceived by this observer will be changing their
motion.