5-DFAC-02

Outcomes

• Pupils should know how to measure average speed practically including an understanding of how a light gate measures velocity.
• Pupils should be able to recall and use the relationship:

<math>a = (v - u)/ t</math>

• Pupils should have an appreciation for how a light gate measures acceleration using a double interrupter or a picket fence.

Specification References

• 1.3 recall and use the relationship between average speed, distance moved and time:

<math>avg speed = distance moved/time taken</math>

• 1.4 recall and use the relationship between acceleration, velocity and time:

<math>a = (v - u)/ t</math>

Starter

Using a ticker timer

• Introduce the ticker timer.
• Discuss the frequency of the dots. This will require some revision from waves (f=1/T) Work out the time period between each set of dots
• With a demo ticker timer produce one tape of a relatively slow steady speed.
• Discuss the tape.
• Proceed in cutting up the tape. Cut at the start. Then cut 5 spaces over and cut again. Ask them how that you work out how far the object travelled in that time. Allow a pupil to measure its length.
• How much time passes over 5 spaces? (t=0.1s)
• Have them work out its average speed over this section.
• Proceed to cut the constant speed tape every 5 spaces and line them up. What do they notice?
• What does the height of each tape represent? Have them calculate the speed of the trolley in one other section. Is it the same?
• What would happen if you pulled the tape through more quickly but at a steady pace. Demo this. Cut this out and place it on the axis.
• How fast is the object travelling now?
• Have them go onto produce three more tapes. One showing steady acceleration, one with greater acceleration and the last showing steady acceleration followed by deceleration.
• Hand out copies of the sheets for them to tape their runs to. There are copies of the first two scenarios at the top and room for them to add their two runs at the bottom.
• Allow them to cut out and tape their three runs below.
• Spend time labelling the five graphs.
• Drawing gradients and linking this to change in velocity over time and therefore acceleration may be beneficial that this time and will lead into the next activity.

Main Body of Lesson

Using The Light Gate

• Run a trolley down a ramp (without an interrupter) and through a light gate. Ask the pupils how a light gate measures the speed of the trolley. Passing your hand through the light beam slowly and then quickly may help them to understand that the time will be measured in that way. Hold up an interrupter. Pass it through the light gate. What does the computer need to calculate the speed? Have a pupil measure the width of the single card. Enter that into the program and take several readings of the speed of the trolley down the ramp. Try a different size interrupter if there is time. Have a pupil enter its width. Show them once again how the speed is obtained in Data Studio. Hold up the picket fence. Ask them how this works.
• Going back to The Journey hand out, ask the pupils in what portion is the train accelerating? decelerating? How do they know? What is acceleration? How would it be measured? The key is for them to understand that the change in speed is needed, and the time for that change. How can a light gate measure acceleration? Introduce them to a double interrupter. Write the formula for acceleration on the board. Use the symbol v and u for final and initial speed. Write the formula again but sub in the speed formula for v and u. What time does the computer use to find the speed? What time does the computer use to find the acceleration? Go onto the picket fence again. Try this with the trolley and the ramp. Measure the cars acceleration. Show them how this is done on Data Studio. Will the acceleration be different if the ramp is tipped more?
• Show the pupils how three readings of acceleration can be obtained very quickly by releasing and catching the trolley just after it passes through the gate.
• They will be measuring the acceleration in the Newton's Second Law experiment and they need to be comfortable with the program and understand the need to take three quick successive readings.

Plenary

• You could go back to the ticker tape graphs and ask them what the area represents? This is a nice visual way to see that the total length (distance) of the tape is in the area of the graph and lead nicely into the next lesson on velocity-time graphs.

Homework

Acceleration Question Sheet

Additional Information

Resources Required

• Motion sensor and large board
• Trolley, ramp, light gate,picket fence, card for interrupters, cellotape.
• Turntable with three different coloured balls tied at different radii.
• Globe with two plasticine people stuck at equator and on England. Do we have one that turns by itself?

Textbook References

• None

Website References

• None

Skills Addressed

• Obtaining

Notes

• None

Forces & Matter Outline

Forces & Matter