Background Information and Demonstrations: Grade Five, Goal 4

Forces and Motion in Technological Designs

Inertia (applications)

Remember, the idea of inertia suggests that moving objects will keep traveling in a straight line at the same speed unless acted on by an outside force. What about things that travel in an arc?  Sometimes, the actual movement of something results from a combination of the effect of inertia and the effect of some other force or forces.

• Drop keys while running

• Egg dropped from a moving car

• Ballistics car

In each of the cases above, we have been defining the motion of an object relative to some frame of reference, so let's take a look at a few demonstrations which explore this idea some more.

Relative Position and Relative Motion

• Path of a ball thrown in a moving van:  Look at the ballistics car demonstration.  What motion would the ball have seemed to make from the perspective of a person riding on the car?
• Relative position and motion with dolls

 
• Circular motion (turntable):  If you lived on a spinning disk, what would it look like if something flew across the sky in a straight line relative to the rest of space?

Motion

• Person riding overhead cart:  distance, speed, acceleration

Since things tend to keep doing what they are already doing, it's worth analyzing what is happening when they change states (speed up, slow down, get moving from a stop, etc.).  For this, we need to develop a concept of energy.
 

Conservation of Energy:  Energy cannot be created or destroyed; it may change forms, but the total amount of energy never changes.

• Rolled ball stops:  Where did the energy go?

• Gyrorings: Why do they keep going?

It is useful to categorize the forms in which we might find energy stored:

Forms of Energy

• Gravitational Potential Energy: Energy stored because something can fall.
• Kinetic Energy:  Energy of movement. Sound energy is included here, since sound is caused by the movement of molecules.
• Elastic Potential Energy:  Energy stored by deforming a material into a non preferred state, such as stretching a rubber band.
• Electrical Energy:  The energy of flowing charges.
• Chemical Potential Energy:  Energy stored in chemical bonds (such as in food), released in chemical reactions (such as metabolism).
• Radiant Energy:  The energy in light or other electromagnetic radiation.
• Nuclear Potential Energy:  Energy that can be released in nuclear reactions, such as in a nuclear reactor or on the sun, in which matter is converted to energy.

Gravitational Potential Energy vs. Kinetic Energy (and remembering conservation of energy)

• Pendulum:  does not hit my nose!

• Superball: No matter how great a superball is, when dropped and left to bounce, it bounces less each time.  Why is this?  Why does it eventually come to rest?

• Astroblaster:  where did the energy come from to make these balls fly?

Conservation of Energy Continued

• Self-propelled vehicles

© Appalachian State University
Science Education On-line
Dr. Leslie Bradbury and Mr. Jeff Goodman