Do Now for 4/24/13

Take out E77 and 78HW: 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!