Lecture # 22 SCIENCE 1 ASSOCIATE DEGREE IN EDUCATION Graphing Motion

Graphs and Presentation Discuss Student’ findings and conclusions. Give each group 10 minutes to discuss its data in response to the task and the questions You might want to add free-body diagrams to their task for additional practice.

Group Presentations Instead of having each group present its findings, you can save time by asking for volunteers. Then discuss that group’s presentation with the rest of the class. For instance, after each group’s presentation, you might ask questions such as: 1.Do you all agree with the findings and explanation of this group? 2.Why or why not? 3.Did you obtain similar or different data? 4.Why do you think you have the same/different data?

Gravity: A Force At this point in the unit, make sure all Students understand that one major force in nature is gravity, which is an attractive force between matter. Earth creates a strong gravitational force that pulls everything towards it. When they place their car on top of the ramp, they lift it, giving it potential energy. When they let it go, the pull of gravity causes it to move faster and faster down the ramp, gaining more and more momentum. The higher the ramp, the more potential energy the car has, and the more momentum it will have when it reaches the bottom.

Exploration and Discussion Also at this point of the exploration and discussion, introduce Students to the term acceleration. The steepness of the ramp influences how rapidly a car accelerates. (They might have experience from bicycling down steep hills.) The steeper the incline, the more rapidly a car accelerates. However, the explanation is not that simple. Listen carefully to how they explain the forces acting on a car that is standing still on top of the ramp. Then listen carefully when they explain what happens to the car when it moves down the ramp.

Can they explain that the gravity acting on the car is always the same, but how the pull is distributed depends on the path? When the ramp is flat, gravity only pulls the car towards the ramp, and the ramp pushes back with an equal amount of force (normal force), so the car stands still. When the ramp is tilted only a small amount, the force of friction keeps gravity from moving the car. If the ramp is steep enough, the frictional forces cannot balance the downward pull of gravity Exploration and Discussion

As a result, the forces are unbalanced, so the car rolls down the ramp. The steeper the ramp, the less gravity pulls the car towards the ramp, and the more gravity pulls the car down the ramp. Therefore, the car has a greater acceleration down the ramp and reaches the bottom with a greater speed. Exploration and Discussion

As Students try to explain these concepts, help them understand by drawing the associated force or free-body diagrams for the different scenarios on the board. Also, let them know that acceleration is a change in speed of an object. (It can go faster or slower and is referred to as positive or negative acceleration, respectively.) Exploration and Discussion

If you can, leave at least 20 minutes at the end of the session to show Students how to convert their data into a visual representation using a graph. Graphing data is a very useful skill in science, and this unit is an ideal context in which to work with data. Data from the classroom might not be sufficient to capture the car’s speed at the beginning of the ramp, at the bottom of the ramp, and then in successive intervals. Therefore, you might want to take the class outside (if possible) for additional data collection. Using longer and higher ramps, the car will travel for a longer duration and distance, allowing for more data collection. Exploration and Discussion

Make sure all Students understand how ‘speed’ is measured. For easier data collection, capture the speed by measuring how long it takes the car to cover a distance of 5-metre intervals. Exploration and Discussion

Students with more prior knowledge in science, math, and graphing should be able to plot the data in a distance vs. time graph. The y-axis is the distance in metres, and the x-axis is the time in seconds. A distance vs. time graph shows how far an object has moved over time. The resulting graphs illustrate nicely the motion of the object: 1.The steeper the graph, the faster the motion 2.A linear graph means constant motion (balanced forces acting on an object, which is Newton’s first law of motion) 3.A non-linear graph means positive or negative acceleration (Newton’s second law of motion) 4.A horizontal line means the object is not changing its position. It is not moving; it is at rest Exploration and Discussion

The Graph

Graphing This graphing exercise is not easy and might not be possible with all Students. If they struggle with graphing, have them calculate the speed of the car (first have them convert their data into metres/second) and then plot the speed (y-axis) over time (x-axis). At a minimum, they should see that the car accelerates until it reaches the highest speed at the bottom of the ramp. Then it slows down again (negative acceleration) as the frictional forces make the car slow down until it comes to a standstill.