Do Now for 4/24/13
Take out E77 and 78
HW: None
E79 Inertia Around a Curve
• Today’s Target: I will be able to see how
inertia affects how an object moves.
• Check HW
• Go over E78 Analysis
• E78 Key Points
• Check E77 and 78
• Introduce and write up E79
• Gather Data (student sheet 79.1)
E79 Inertia Around a Curve
• Which type of car, a heavier or lighter one,
needs more force to slow down with the
same deceleration?
– It is harder for the heavier car to slow down
because it needs more force to decelerate.
– It has more mass, so it needs more force to
change its speed.
E79 Inertia Around a Curve
• Inertia – The tendency of an object to
continue to move at the same speed and
direction it is currently moving.
– NOT A FORCE, it is a way to describe the
movement of objects.
– Objects at rest will remain at rest unless acted on
by another force.
E79 Inertia Around a Curve
• Open books to page E-25
– Read background and write up.
– Take out Students sheet 79.1
• This activity will depend upon your
AWESOME observational skills!
• Review steps 1 through 7
– Demonstrate Step 2
– Demonstrate Step 5 and Step 6
• Gather data for Part A and Part B
Do Now for 4/25/13
• Take out E79 Report and sheet 79.1
• HW: Complete analysis
E79 Inertia Around a Curve
• Today’s Target: To see how a curve affects
the inertia of an object.
• Complete gathering data for Part A and B
• Discuss results
• Analysis 1 through 3
• Key Points
E79 Inertia Around a Curve
• Do the marbles continue around the curve?
– No
– They follow a straight line path as soon as they
pass into the opening in the track.
E79 Inertia Around a Curve
• 1. Describe the changes in direction and
speed of the marbles when they traveled
• a. inside the circular track?
– The marbles’ direction changed constantly inside
the circular track because of the force the wall
exerted on the marble. Similarly, the surface of
the circular track rubbed on the marble and
slowed it down slightly.
E79 Inertia Around a Curve
• b. outside the circular track?
– The direction once outside the circular track was
in a straight line, moving across the table. The
speed slowed slightly because of the table
surface rubbing on the marble.
E79 Inertia Around a Curve
• What force:
– Accelerated the marble from rest?
• Your hand
– Makes the marble travel in a circle?
• Inside wall of the circular track.
– Makes the marble slow down?
• Table surface, friction in the track, air, etc.
E79 Inertia Around a Curve
• 2. Describe any changes in the path of the
marble that occurred when you changed the:
• a. opening position of the circular track.
– The marble left the opening in a different direction
for each opening position. Once it left the circular
track, however, it continued in a straight line.
• b. mass of the marble.
– When comparing the glass (lighter) marble to the
heavier (metal) one, no changes occurred to the
direction that the marble traveled.
E79 Inertia Around a Curve
• Remember, inertia describes the tendency
(and not the force) of an object to keep going
in a straight line at a constant speed even
when there are no forces acting on it.
• How would the results change if there were
no friction?
– Marble would travel in a straight line for ever.
E79 Inertia Around a Curve
• think of a time when you were in a car that
made a fast turn around a corner or went
around a sharp curve quickly, and to describe
what it felt like.
– Most people will say their bodies were “pushed” or
“pulled” toward the outside of the curve, and some
will even report that they slid or bumped into the
side of the car or the person next to them.
– Your bodies’ inertia kept you going straight while the
car turned.
E79 Inertia Around a Curve
E79 Inertia Around a Curve
• 3. Imagine that a car is approaching a curve
in the road when it suddenly loses its steering
and brakes. The area is flat and there is no
guardrail on the road.
• a. Copy the diagram below in your science
notebook. Then draw a line showing the car’s
path when it loses its steering and brakes.
E79 Inertia Around a Curve
E79 Inertia Around a Curve
• b. Explain why the car will take that path.
– Because of inertia, which in the absence of other
forces keeps moving objects moving in a straight
line.
• c. How would your answer change if the car
had more mass? Explain.
– More mass will not change the direction the car
travels. It would, however, affect the force
needed to stop the car.
E79 Inertia Around a Curve – Key
Points
• 1. An object that is not being subject to a
force will continue to move at a constant
speed in a straight line.
• 2. Scientific explanations emphasize
evidence, have logically consistent
arguments, and use scientific principles,
models, and theories.
• Cool science trick using inertia to try at
home!