Engage: On the Subway

Take a moment to watch the video below. Try not to laugh!

SubwayFall.mp4

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Source: 
Video courtesy of: http://www.youtube.com/watch?v=626QX3tukLQ

Has that ever happened to you on the subway, the train, or even in a car?

What happened in the video? What do you already know that might explain this phenomenon?

Explore: Horsing Around

Watch the video below and collect data on what is happening. You probably will have to watch the video more than once during your data collection.

8.6Cfirst.mp4

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Now that you have collected your data, respond to the questions below.

1. Where did the girl land? Why?

2. Would she land in the same place if she had more mass? What if she had less mass?

3. Is the video scientifically similar to or different from the video of the woman on the subway? Why or why not?

Explain: Newton's Law of Inertia

The woman on the subway fell forward because of inertia, the tendency of an object to keep doing what it's doing unless acted on by an unbalanced force. Both the woman and the subway car were traveling at the same speed. When the subway car stops suddenly, the woman is still moving at the same speed and falls forward. This is similar to what happened with the girl on the horse. The girl and the horse were moving at the same speed in the same direction until the horse changed direction and speed. The girl continued to move forward while the horse stopped and moved to the right. What if the girl had more mass or less mass? 

  • If the girl had more mass, she would have had more inertia. This would mean that as the horse stopped, she would not have moved as far as she did in the video.
  • If the girl had less mass, she would have had less inertia. This means that as the horse stopped, she would have moved farther than she did in the video.

To recap, Newton's first law, the law of inertia, states the following:

An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted on by an unbalanced force.

Newton's law of inertia is involved when car accidents happen. The car and its occupant are traveling at the same speed—let's say 40 miles per hour. If there is a small amount of force on the car, such as pressing the brakes slightly, the occupants feel themselves fall forward a bit. If there is a large amount of force on the car, such as slamming on the brakes, the occupants feel themselves fall forward even more. There is a direct relationship between how great the unbalanced force is and how great the change in speed and/or direction is. 

Sometimes, seeing a few more examples helps to better understand. Click the Image of Sir Isaac Newton below. When the new website loads, press the green "Play Video" button to see an addition explanation.

Let's check your understanding with a short interactive quiz!

Elaborate: Newton and Football

Do you still think Newton's law of inertia doesn't apply to real life? Think again! Watch the video below to see how Newton's first law applies to football. Click on the football below to view the video.

Teacher Notes

This resource is a compilation of text, videos, and other elements to create a scaffolded 5E learning experience for students. This is meant for Tier I instruction under the Response to Intervention (RtI) model for grade 8 science TEKS (6)(C), specifically Newton's law of inertia.

Be sure to check for prerequisite knowledge and skills as well as differentiation needs by reviewing the entire resource and the related items before assigning it to or working through it with your students.

This resource can be used for instruction in a variety of ways.
• Use with a single computer and projector; this resource can be delivered in a traditional classroom.
• Use with a combination of individual student computers and teacher computer and projector (in either a computer lab or other 1:1 environment).
• Assign the resource to students as work to do outside of the school day as part of a "flipped classroom" to allow application, practice, and additional support during the school day.
• Use with students as tutorials.
• Share with parents to inform them about what their child is learning in school.
• Use with students who are unable to participate in the traditional classroom environment.


Engage
Students view a video of a woman nearly falling when the subway car suddenly moves. This video should get students thinking about why this happens when a vehicle, such as a subway car, suddenly moves or stops.

Classroom Options
• Have students view the video and do a think-pair-share about what is happening and what scientific phenomenon is causing it. Have students record their thoughts in their science notebooks.
• Instruct students to brainstorm other occasions where this occurs and then compare and contrast these situations to explain what is happening.


Explore
Students collect data by watching a video of a girl falling off a horse. Students will observe that the horse stopped but the girl in the video kept moving in the same direction. Consideration is made here for situations where the rider might have more mass or less mass and the possible connection to inertia.

Classroom Option
• The same data could be obtained by allowing students to use small toy cars and different size washers to investigate how far the washers travel when the car stops suddenly. Students put the washer on the roof of the toy car and then stop the car suddenly and measure how far the washer travels from its position on the roof of the car.

Explain I
The Explain connects students' observations and data collection from the Engage and Explore with the concept of Newton's first law, the law of inertia. It is important that students have many real world applications to build understanding, so there are also connections made to car accidents. The Related Items section has a video that elaborates on Newton's law of inertia as it applies to car accidents.

Elaborate
The video in the elaborate makes connections to professional football and Newton's law of inertia. The teacher is welcome to make any additional connections that will make the law of inertia relevant to his or her students.