Lesson Plan Template: General Lesson Plan
Learning Objectives: What should students know and be able to do as a result of this lesson?
Students will be able to identify situations that relate to Newton's Third Law.
Students will be able to understand that if an object is pulling or pushing another object, the forces each one exerts on the other one act simultaneously, in the opposite direction, and are equal in magnitude, no mater the direction of the motion or if the objects remain still.
Students will able to understand that action reaction pairs act on different objects.
Students will able to identify action reaction pairs in different situations.
Prior Knowledge: What prior knowledge should students have for this lesson?
Students should be familiar with the following concepts:
- Gravitational Acceleration
- Newton's First and Second Laws
- Force diagrams
- Free body diagrams
- Students should be familiar with the use of the force sensor and data collector
Guiding Questions: What are the guiding questions for this lesson?
What we can say about the forces two objects exert on each other when one object is pulling or pushing the other one?
Teaching Phase: How will the teacher present the concept or skill to students?
The teacher will ask students the following question:
A horse is pulling a cart at the speed 20 Km/h. Which is the correct statement about the forces acting on the cart and on the horse?
a) The force the horse is exerting on the cart is larger than the force the cart is exerting on the horse.
b) The force the horse is exerting on the cart is smaller than the force the cart is exerting on the horse.
c) The force the horse is exerting on the cart is equal in magnitude to the force the cart is exerting on the horse.
d) The horse is exerting a force on the cart but the cart is not exerting a force on the horse.
The typical misconception is that if the horse is actually moving the cart, it is exerting a larger force on the cart than the cart is exerting on it. The teacher will come back to this question at the Closure to verify their understanding and clarify the misconception.
Guided Practice: What activities or exercises will the students complete with teacher guidance?
The teacher will present the following questions to the students:
- A balloon filled with helium is pulling upward on a 2 g cylinder. What we can state about the forces involved in this situation?
- A balloon filled with helium is pulling upward on a 1 kg cylinder. What we can state about the forces involved in this situation?
Students are going to express their opinions and make a hypothesis.
The students will investigate each of the questions.
The teacher will provide students the equipment they need.
The students will set up the equipment in order to investigate the given problem addressed in the 'Teaching Phase' section.
Students will reproduce the force vs. velocity graph from the data collector on graph paper.
Students will identify what forces are the ones represented on these graphs.
Independent Practice: What activities or exercises will students complete to reinforce the concepts and skills developed in the lesson?
As homework for the next class, the students will write three examples in which the Newton's Third Law is applied.
They will have to describe the situations, identify the action reaction pairs, include the force diagrams of the two interacting objects, and the free body diagrams of each object.
Closure: How will the teacher assist students in organizing the knowledge gained in the lesson?
Most of the students have some knowledge about Newton's Third Law. The most common definition they know from Middle School is that for every action, there is an equal and opposite reaction.
As a conclusion, the teacher will ask students to define Newton's Third Law in one short paragraph in their own words. The teacher should advise students against using the text book or internet to find the definition.
The teacher will ask students to exchange their papers and some students will read the anonymous definitions. Cooperatively students will discuss if the definitions miss anything or state something incorrect.
The teacher will write the definition of Newton's Third Law such as the one here or in your student textbooks (The Physics Classroom) on the board. Then ask students to copy it on their notebooks.
The teacher will present again the question about the horse pulling the cart that was given at the beginning (Teaching Phase) to verify the students' understanding.
The teacher will ask some students to solve on the board the following questions:
- Draw the force diagram for the system horse/cart floor (they have to include all the forces).
- Draw the free body diagram for each one of the components of the system.
- Identify the action reaction pairs present on the force diagram.
Students should be able to identify the following action reaction pairs:
- The force exerted by the horse on the cart and the force exerted by the cart on the horse.
- The force exerted by the horse (equal to its weight) on the floor and the force exerted by the floor on the horse (normal force).
- The force exerted by the cart (equal to its weight) on the floor and the force exerted by the floor on the cart (normal force).
- The fiction force exerted by the horse shoes on the floor (backwards) and the friction force exerted by the floor on the horse shoes (forward).
- The friction force exerted by the floor on the cart wheels (forward) and the friction force exerted by the cart wheels on the cart (backwards).
- Ignore air fiction and internal frictions on the cart.
As a conclusion of the activity, each group will present their forces vs time graphs for the two different scenarios on a 2'x2' white board and will make as many observations as they can about the graphs. The observations should include the direction and magnitude of the force vectors at different instants and the comparison and contrast of the two different scenarios.
Students would expect force vs. time graph showing two parallel lines as a result of a constant force exert by the balloon on the cylinder (positive), and an equal in magnitude but negative force exerted by the cylinder on the balloon. However, for different reasons, the graph still will show that the forces are equal and opposite at any instant, but not necessarily constant (probably the graph will show some spikes)
When comparing the two graphs, the one of the balloon lifting the cylinder with the one of the balloon and the cylinder still, students should realize that on the first scenario the action reaction forces are larger than the weight of the cylinder plus the weight of the force censor, and on the second scenario, the action reaction forces are smaller than the weight of the cylinder plus the weight of the force censor.
The teacher could ask students about the spikes on the graphs. The spikes could take place because the cable of the force censor is exerting an extra non-constant force.
After the student presentations, show the students the video on how rockets work. http://www.youtube.com/watch?v=cP0Bb3WXJ_k
Students will be graded using the attached rubric. Grading Rubric
The teacher will present a specific question related to Newton's Third Law. Students will have the opportunity to express their opinions and make a hypothesis. The teacher will divide students into groups of 5-6. Students in the same group don't need to have the same hypothesis. Students will design an experiment to test their hypothesis.
Each student will present a Lab Report. On the report the students are going reproduce the forces vs time graphs for the two different scenarios obtained on the data collector (VERNIER or PASCO), and will write comments about the interpretation of graphs including the difference between the two scenarios. In addition, students will make force diagrams and free body diagrams for each scenario.
Feedback to Students
The teacher will give feedback to each group after their presentations.
The teacher will ask each group to answer the initial question. The teacher will not deny or confirm any of the answers until the last group presentation.