What should know about constant velocity and the physical quantity of velocity at the end?
1) Velocity is the rate of change in an object's position.
2) Velocity has two parts, speed and direction.
3) Different forms of representation (i.e motion diagrams, graphs and mathematical representation ).
Describe how you help your students construct the ideas of motion with constant velocity, and the physical quantity of velocity.
It is important that students know the difference between position and displacement, so start with motion as a change in position. Do an observational experiment with an object moving at constant speed. Roller blades work well for this. How does the motion change? How can it be quantified? You want students to develop the idea that the motion is described by position and time.
Students need a tool to help them analyze motion. Developing this tool can either be done as part of the previous experiment or the next. In either case you will need an experiment where position can be marked at regular time intervals. (For example a rollerblader marks a chalk board every second.)
Students should now do a quantitative experiment with an object moving with constant velocity. Have students do a motion diagram and then plot position vs. clock reading. Have the students develop a mathematical relationship between position and clock reading. What is the meaning of the slope? (the velocity, for constant velocity this is the displacement per unit time.) What are the lengths of the arrows in the motion diagram? Have students plot v vs. clock reading. What does this tell you about the velocity? What is the area under the curve? (the displacement) (Notice this is an important step that prepares for the discussion of acceloration.)