5-FAC-02

Outcomes

• Pupils can interpret velocity-time graphs including zero velocity, constant speed, constant acceleration, constant deceleration and have an appreciation for changing acceleration and negative velocity.
• Pupils should be able to sketch a velocity-time graph from a distance-time graph. They should be able to pin point key areas starting with zero velocity regions.
• Pupils should be able to calculate the gradient of a distance-time graph to work out the speed in order to add a scale to a sketched velocity-time graph.
• Pupils should be able to calculate the gradient of a velocity-time graph to work out the acceleration. They should appreciate that the shape of velocity time graphs indicate if the acceleration is zero, constant or changing.
• Pupils should understand that the area under a velocity time graph gives the distance travelled.
• Pupils should be able to sketch a velocity-time graph for a person jumping from an aircraft. They should appreciate the sections where the person is accelerating and not accelerating and what this means in terms of the forces acting on them.
• Pupils should understand that acceleration comes from an unbalanced force.
• Pupils should appreciate that speed, mass, road condition and reaction time are the factors that affect vehicle stopping distance.

Specification References

• 1.5 interpret velocity-time graphs
• 1.6 determine acceleration from the gradient of a velocity-time graph
• 1.7 determine the distance travelled from the area between a velocity-time graph and the time axis.
• 1.16 describe the forces acting on falling objects and explain why falling objects reach a terminal velocity.
• 1.17 describe the factors affecting vehicle stopping distance including speed, mass, road condition and reaction time.

Starter

• Using a motion sensor and Making Velocity-time Graphs
• The pupils extend the exercise from the previous lesson but now try and produce velocity time graphs and linking them back to the distance time graphs. Ask them to cut out and match up the velocity-time graphs with the distance-time graphs from the previous lesson.

Main Body of Lesson

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 two more tapes. One showing steady acceleration and the other 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 two runs below.
• Spend time labelling the four 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.

Sketching velocity-time graphs

• Using The Journey again have the pupils use the last column of the table to work out the instantaneous speed at each step of the train journey. They should do this in groups so that they share out the work between four. This should make this go a bit quicker. From this they make the connection between constant slope being constant speed and horizontal portions being zero speed. Hand out The Journey - sketching velocity-time graphs. This allows pupils to sketch the velocity time graph below the distance time graphs with the time scale in-line. They can use their calculations from earlier to help add values to the y-axis. You can spend time pointing out the key points (horizontal->zero gradient->zero speed, constant slope-> constant gradient-> constant speed, changing slope-> changing gradient-> changing speed-> acceleration, steeper slope-> larger gradient-> greater speed)
• Have the students work out the area of the By Train velocity-time graph. This may require some estimating. What does this represent? Hopefully they will make the connection that the area under a velocity-time graph is the distance travelled. Look back at the data. How far does the train travel? Have them look at the units when they multiply the velocity and the time axis. It is important for them to see that the time unit cancels and they are left with metres.
• Finish with two or three example questions. These start easy and lead into negative velocity and objects travelling back home.
• Extension- Have the pupils sketch a distance time for a bouncing ball. Have them then sketch a velocity time graph from that. Use a motion sensor to show the shape of each graph. It is important to understand the vector nature of velocity and link travelling in the opposite direction to negative velocity below the x-axis.

Plenary

• Sketch a velocity-time graph for a falling object. A person jumping out of a plane.
• Use the sheet-The Jump-to do this. It includes diagrams of a person, to label forces on, at each stage of the jump. This will show when the resultant force is greatest (at the beginning) and when it is balanced (at terminal velocity both without the chute open and with it open). This also points out that the weight vector does not change but the air resistance vector changes in magnitude according to the speed or if the parachute is open.

Homework

• Velocity-time and distance-time graphs question sheet
• Question sheet on Stopping Distance - use of speed = distance/time, using a velocity time graph to work out distance covered with different thinking times and including factors affecting stopping distances.
• Questions 1-3 pg 31

Additional Information

Textbook References

• None

Website References

• None

Skills Addressed

• Obtaining

Safety/Hazards

Risk Assessment

Notes

• None

Forces & Matter Outline

Forces & Matter