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Science Lesson Plan Newton’s First Law Lesson provided by Richard Worsey, Head of Science Faculty Background Once upon a time an apple fell from Sir Isaac Newton’s Tree. I took this photograph of a descendent of this very tree at Isaac Newton’s house, Woolsthorpe Manor in England. Isaac Newton was a famous English scientist. He studied and observed how objects move. He wrote one of the most important mathematics books in history: Philosphiae Naturalis Principia. Newton’s First Law is particularly challenging to students, as it essentially comes in two parts. One part predicts the behaviour of moving objects; the other part predicts that of stationary objects. Difficulties are then further compounded by a link to inertia. My approach is to eliminate some of the misconceptions that surround the law by bringing them to the fore in open discussion. A common misception is that sustained motion requires a sustained force. Another one is that an object is always at rest when the forces are balanced. The key approach in this lesson is to get beyond the law as a statement and to understand its implications and links to motion observed in everyday life. Once the law is better understood, inertia can be brought into play and the law rewritten as a statement of inertia. The associated Boardworks PowerPoint also provides a link to other topics such as interpretation of velocity vs time graphs and terminal velocity. Approach The objectives of this lesson are; 1) To understand and be able to interpret Newton’s First Law of Motion. 2) To demonstrate this understanding by applying it to challenging and novel situations. Equipment required: • ramp and support • spring loaded motion trolley • ball bearing • plasticine • foam • high shutter speed video camera (optional) Boardworks Ltd The Gallery 54 Marston Street Oxford, OX4 1LF • paper • cotton thread • masses for parachute • Loggerpro software or other tracking software such as Tracker. FREE sample material w ww download from k o.u .boa rdworks.c t: 0845 0 300 400 f: 0845 0 300 200 [email protected] www.boardworks.co.uk Science Lesson Plan Newton’s First Law The Activity This activity involves two main parts. First, the students will see and analyse a collision video clip, and then perform two experiments to further study collisions in terms of Newton’s First Law. The second part considers terminal velocity in the context of a parachute falling. Collisions Show an NCAP safety collision video clip – You Tube has a proliferation of these. An example can be found at http://www.youtube.com/watch?v=5VqI IcUDxRI&feature=fvsr Newton’s F irst Law, slid e2 Once the class has viewed the video, ask the students two questions - provide no hints and generate a discussion without correcting any misconception at this stage. 1) Is a passenger thrown forward in a front end car crash? 2) Is a passenger’s head thrown backwards if a car is run into from behind? Once each student has decided on an answer, ask for their justification – again providing no hints as to whether they are correct or incorrect. Show slide 2 (free to download) from the Boardworks PowerPoint ‘Newtons First Law’. Explain (or recap) what is meant by weight and reaction forces. Using the animation on slide 2, discuss how the forces affect each of the motions and how these might change if the size of individual forces is altered. Talk about balanced forces and how these can cause an object to stay at rest or remain at a constant velocity. Use slide 3 (free to download) to summarise this discussion as Newton’s First Law. Newton’s F irst Law, slid Or Boardworks Ltd The Gallery 54 Marston Street Oxford, OX4 1LF d r FREE Sampl You eD r e i e3 sc t: 0845 0 300 400 f: 0845 0 300 200 [email protected] www.boardworks.co.uk Science Lesson Plan Newton’s First Law Without further explanation, offer the students a chance to revise their answers and justifications to the two questions set at the beginning of the lesson based on their new understanding. To further explore these questions, set up the following two experiments. It is useful to video the experiments with a high-speed shutter and then capture frames to explain what is happening in the experiment. Experiment 1: front end crash Set up the experiment as shown in Figure 1. Release the trolley down the slope. Ensure that the ball bearing is free to move within the plasticine dish. As the trolley collides with the foam, the ball continues to move forwards, as there is no resultant force acting upon it. Ask the students to observe the ball bearing. Figure 1. Experiment 2: rear end crash Set up the experiment as shown in Figure 2. Compress the spring and release the trolley. The ball bearing should be free to move as the trolley is released initially. The ball bearing remains stationary, as there is no resultant force acting upon it. Or Boardworks Ltd The Gallery 54 Marston Street Oxford, OX4 1LF d r FREE Sampl You eD r e i Figure 2. sc t: 0845 0 300 400 f: 0845 0 300 200 [email protected] www.boardworks.co.uk Science Lesson Plan Newton’s First Law Figure 3 shows some example frame captures from Experiment 2. 1. Trolley moving left to right just prior to collision. 2. Trolley moving left post collision. Note position of ball bearing relative to wall. 3. Trolley moving left post collision. Note position of ball bearing relative to wall. 4. Trolley moving left post collision. Note position of ball bearing relative to wall. Figure 3. Key concept – an object will remain at rest or remain in motion unless acted upon by an unbalanced (resultant) force. Parachute Another misconception can arise that needs to be dealt with here – an object is always at rest when the forces are balanced. In the context of a skydiver reaching terminal velocity, slides 4 and 5 (free to download) from the Boardworks PowerPoint will address this. Play the parachute animation on slide 4 and discuss with the students what happens as the resistive force alters due to acceleration (this can be related to everyday experience e.g. resistive force as you accelerate downhill on a bike). Use the data produced to graph (slide 5) and discuss what each section of the graph represents. Or Boardworks Ltd The Gallery 54 Marston Street Oxford, OX4 1LF d r FREE Sampl You eD r e i Newton’s F irst Law, slid e4 sc t: 0845 0 300 400 f: 0845 0 300 200 [email protected] www.boardworks.co.uk Science Lesson Plan Newton’s First Law Students can now investigate this for themselves via a parachute experiment. They can make their own parachutes from simple materials such as paper, cotton thread and weights to explore how different factors, such as drag surface area and mass, affect motion. Consider using tracking software to analyse a video of the descent of different parachutes to compare the variables. An alternative to the parachute experiment is to product the graph first from slide 5 and then verify using the Boardworks animation, slide 4. Newton’s F irst Law, slid e5 Taking it Further The natural extension of this lesson is to introduce inertia – the reluctance of an object to move. This can be done by pulling paper from under two cans (one heavy and one light but not telling the students which is which!). Place these cans on trolleys and ask students to push them then relate to inertia. Outcomes/Benefits If the learning objectives have been achieved, students will now understand Newton’s First Law. A good way to check this is to ask the students to rewrite it in a different form. Some ‘thought’ questions for homework: • If you were repairing the Hubble Telescope and pushed away from it to return to your space shuttle how could you create the additional force needed to keep you moving towards the shuttle? • Many cars have headrests. How do these prevent neck injuries? Explain your answer in terms of Newton’s First law. • Explain in terms of inertia why you should zigzag as you run away from an elephant. Or Boardworks Ltd The Gallery 54 Marston Street Oxford, OX4 1LF d r FREE Sampl You eD r e i sc t: 0845 0 300 400 f: 0845 0 300 200 [email protected] www.boardworks.co.uk