5-FAC-01

Outcomes

• Pupils should be able to sketch, draw and interpret a range of distance time graphs which includes zero speed, constant speed and acceleration.
• Pupils should understand the significance of average speed versus instantaneous speed.
• Pupils should be able to use and recall the relationship <math>avg speed=distance moved/time taken</math>
• 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)/ \Delta t</math>

• Pupils should have an appreciation for how a light gate measures acceleration using a double interrupter or a picket fence.
• Pupils should be able to use the relationship

<math>v= (2 \pi r)/T</math>

• Pupils should be able to link the equation above to the orbital speed of planets.
• Pupils need to recall the circumference of a circle equation and the meaning of the term Time Period.

Specification References

• 1.2 understand and use distance-time graphs
• 1.3 recall and use the relationship between average speed, distance moved and time: <math>avg speed = distance moved/time taken</math>
• 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>

• 1.33 use the relationship between orbital speed, distance moved and time: orbital speed = (2 x pi x orbital radius)/time period or <math>v= (2xpixr)/T</math>

Starter

Distance-time graphs using motion sensor

• Using a motion sensor and Making Distance-time Graphs sheet.
• The pupils are presented with a range of distance time graphs and are asked to act them out infront of the class. The middle column is for the pupils to describe in words how they produced the distance time graph.
• The last column will be used in the next lesson when they are asked to link distance-time graphs and velocity-time graphs.
• They should begin to get the idea of zero speed is horizontal, constant speed is a straight line and that the gradient of the line indicates its magnitude. In addition a change gradient means changing speed which is acceleration. Negative gradient is speed in opposite direction!

Main Body of Lesson

The Journey- using a distance-time graph

• Brain storm: What is speed? What is velocity? What is the difference between them? Revise vector and scalars.
• Discuss how the speed of car can be measured. What equipment would one need?
• Hand out a copy of The Journey, which includes data for two journeys From Reigate to Redhill. One by train and the other by bus. The train is going directly to the destination without stopping and the bus is required to stop several times to pick up other passengers. The questions require them to assess each journey. They begin by working out the speed in several portions of the journey and then describing each journey in words. They end by calculating the average speed for the first and second half of the journey for each mode of transport and the overall average speed of each journey. The bus requires some walking either end to get to or from the stations and is included in the data. This will allow them to appreciate the meaning of average speed and instantaneous speed. This can be extended by drawing the distance-time graphs. They are copies of them if you have no time to do this.
• What is the difference between average speed and instantaneous speed?

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

Orbital Speed

• Demo the turntable with objects (different coloured balls) orbiting at different radii. What is the orbit time? Link this to Time Period, T.
• How does the Time Period compare for each object? How about their speed?
• How can the speed be measured?
• How do you work out the distance travelled by each object? Have a student measure the radius of one orbit. Have them sub these into the average speed formula to derive the orbital speed equation.
• How can we measure the Time Period? This gives the opportunity to discuss the benefit of multiple readings and timing more than one revolution.

Challenge

• Have plasticine people stuck to the globe at both the equator and on England.
• Orbital Speed Challenge - Ask the pupils to work out the orbital speed of each person. They must be provided with the radius at each latitude.
• What is the Time Period for each orbit/revolution? It my be better to work out the speed in km/h as they get more a sense of just how fast they are travelling. They could convert to m/s just to practice conversions.
• Finish by asking them what the orbital speed would be if they were stood at the poles?

Homework

• Distance-time graph questions
• Speed and 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