Unit: Newton’s Third Law

Grade: 9-12

Content Area: Science

Course Name: Physics

Description of Unit: In this unit, students will explore Newton’s Third Law of Motion and Momentum concepts. The relationship between impulse and momentum will also be made by the students.

Approximate Time Needed: 7-10 days

Benchmarks:        5.1 I can use vectors and free-body diagrams to describe force, position, velocity and acceleration of objects in two-dimensional space. (9P.2.2.1.1)

        5.2 I can recognize that inertia is the property of an object that causes it to resist changes in motion. (9.2.2.2.1)

        5.3 I can apply Newton’s three laws of motion to calculate and analyze the effect of forces and momentum on motion. (9P.2.2.1.2)

        5.4 I can explain and calculate the acceleration of an object subjected to a set of forces in one dimension (F=ma). (9.2.2.2.2)

        5.5 I can demonstrate that whenever one object exerts force on another, a force equal in magnitude and opposite in direction is exerted by the second object back on the first object. (9.2.2.2.3)

        5.6 I can use conservation of momentum and conservation of energy to analyze an elastic collision of two solid objects in one-dimensional motion. (9P.2.2.2.3)

        

Essential Questions:         How will a change in the force affect the momentum of an object?

        How does the interaction of two objects change the state of motion for each?

Lesson

Duration

Supporting Target

Resources

Assessment

1

2-3 days

I can apply Newton’s three laws of motion to analyze the effect of forces and momentum on motion.

Effects on Impact Project

Pre

2

2-3 days

I can use vectors and free-body diagrams to describe force, position, velocity and acceleration of objects in two-dimensional space.

I can apply Newton’s three laws of motion to calculate and analyze the effect of forces and momentum on motion.

I can explain and calculate the acceleration of an object subjected to a set of forces in one dimension (F=ma).

I can demonstrate that whenever one object exerts force on another, a force equal in magnitude and opposite in direction is exerted by the second object back on the first object.

I can use conservation of momentum and conservation of energy to analyze an elastic collision of two solid objects in one-dimensional motion.

Third law presentation

Momentum presentation

Third Law and momentum worksheet

Pre

Formative

3

1 day

I can collect data from a video.

I can use the Impulse-Momentum Theorem to solve problems.

I can use the Conservation of Momentum to solve problems.

Impulse-Momentum Video Lab 

Formative

4

1-2 days

I can use a free body diagram to describe the motion of an object.

I can use conservation of momentum to analysis an elastic collision

I can use the Impulse-Momentum Theorem to analysis an elastic collision.

I can relate an experiment to the theories of impulse and momentum for collisions.

Impulse-Momentum Lab - Student 

Impulse-Momentum Lab - Presentation

Summative

5

1 day

I can use free body diagrams to describe the motion of an object.

I can apply Newton’s Three Laws to calculate and analyze the effect of forces on the momentum of an object.

I can demonstrate Newton’s 3rd Law of Motion.

I can use the conservation of Momentum to analyze the collision of objects.

Fictional Physics - Blown Away

Student Worksheet

Summative

Activity

Notes to Instructors

Assessments

As in previous units, this document contains a question bank for 2 formative and 1 summative assessment.

Effects on Impact Project

Purpose: To get the students thinking about impulse and momentum in their own terms before introducing it to them.

Materials: This is a student designed lab, so the materials needed will vary.

Notes to instructor: Having digital sensors for this lab is nice, but not necessary. The trickiest thing to measure for the students is figuring out how they are going to measure the “Effect of Impact”. I have had students do this in many ways in the past:

  • Use of spring scales
  • Use of force sensors
  • Looking at depth of depression left in clay or some other easily deformed material.
  • Looking at how far back an object such as a book was pushed.

This is a good activity to get students thinking about how factors relate to each other and how to measure difficult quantities and communicate results to others in a meaningful way.

Time: 90-135 minutes depending on to what extent you will expect students to work on this outside of class.

Third law presentation

Slide 3: Some examples include: body - chair; hand - pencil; book - desk

Slide 4: thrust - drag; lift - weight

       The forces are equal in magnitude, but opposite in direction; Fnet = 0 N

       Drag is greater in magnitude than thrust

Time: 30 minutes

Momentum presentation

Slide 2: Momentum is a vector quantity because velocity is a vector quantity (p = m * ∆v)

Slide 3: Impulse is a vector quantity because force is a vector quantity (J = F * t)

Slide 6: For every action, there is an equal and opposite reaction.

       You move backwards and the rock moves forwards.

       The ball would move with a greater velocity, because logically it would have less mass than you. Mass and

       velocity are inversely related.

       Video shows and explains conservation of momentum in collisions of football players.

Time: 30 minutes

Third Law and momentum worksheet

1. 26,000 kg•m/s north

2. 14 m/s

3. 45 kg•m/s & 6.1 m/s

4. 4.0 kg•m/s & 28 m/s

5. 27 N

6. 2.5 s

7. A. 2.1 m/s east B. 2.0 m/s east C. 1.4 m/s east

Impulse-Momentum Video Lab

Purpose: This lab is used to help students better understand the concepts of Impulse and Momentum. Students will be using Direct Measurement Videos - Impulse and Momentum to collect data and perform calculations. Students will be able to use Quicktime as done in similar activities. Directions for downloading the videos to the student’s computers is on the page. A discussion on the number of significant figures could be part of this activity as well to establish certainty in measurements.

Ipad Option: You can download the videos and put them in a dropbox to share with the students. Once they have the video saved in their camera roll, data can be collected by opening the video and scrolling the playhead at the top. Students will have to watch the frame and may need to make notes on which one they are on.

Hockey Slap Shot: Final answer is 140,000 N. From the video there is about 9 frames of contact at 240 fps for a time in contact of 0.038 s. The mass of the puck is 169.7 g. The velocity after the shot is about 32 m/s and found by using a combination of distance and frames. The initial momentum of the puck is 0 kgm/s and final is 5400 kgm/s.

Collision Cart Push-off: In this video, students are looking at the conservation of momentum. The total momentum before the push is zero so the momentum after the push should also be zero. Treat Damon’s momentum as positive and Christine’s as negative. It takes Christine 37 frames or 0.15 seconds for a speed of 1.3 m/s where Damon uses 41 frames or 0.017 seconds for a speed of 1.2 m/s. Damon’s momentum is 104 kgm/s and Christine’s is -104 kgm/s. The law is conserved when we round to the reasonable significant figures. An extension question could be to ask the students what would cause the momentums to not be the same. One possible reason would be shifting of each person’s body during the push.

Blowdart Cart Collision: Final answer should be about 28.4 g. The dart covers about 25.8 cm in 10 frames and it takes 19 frames for the cart to move the 5 cm. Using conservation of momentum will yield the answer. This video will display the inelastic collision for momentum.

Time: 30-40 minutes.

Impulse-Momentum Lab - Student 

Impulse-Momentum Lab - Presentation

Purpose: This lab activity is used as a way for students to display their understanding of the conservation of momentum and the Impulse-Momentum Theorem. The collision that is analysed will be created by the student. You will not be looking for perfect correlation with the experiment, in fact it would be better to see the data/calculation not fit. This would allow for better explanations of the concepts and display a better understanding.

With the lab design open to the student, they will need to consider all of the values needed to discuss the conservation of momentum and the Impulse-Momentum Theorem. Look for the masses of the objects, velocities of the object and the time in contact during the collision.

Videos of the collision could be used. If this is the case, students can make use of Video Physics for the iPad or Logger Pro or Tracker for the computer. The biggest point of error for this will be the limited frame rate of the camera taking the video.

Time: 80-100 minutes over several days.

Fictional Physics - Blown Away

Student Worksheet

Teacher Guide

As in all fictional physics. Students are asked to use physics concepts to evaluate a situation from fiction, in this case being thrown back by a bullet.

Time: 45 minutes

PHYSICS by MN Partnership forCollaborative Curriculum is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.