2003 Virginia SOLs
Motivation for Learning
Discrepant Event - Tablecloth yank
Place tablecloth over table with the majority hanging over one side. Set the table and fill the wine glass. Grasping the hanging cloth firmly, jerk quickly downward and away from the table. With practice this will leave the table setting untouched and the cloth off the table.
Discrepant Event - Hanging Mass
Tie a piece of string to the top of the mass and then tie that to a ring stand so that the mass is suspended. Tie another piece of string to the bottom of the mass. If you yank the bottom string quickly, that string should break. If you pull the bottom string and constantly (and fairly slowly) increase the force, the top string should break.
Newton's First Law of Motion states that an object at rest will remain at rest unless an external force acts upon it. Similarly, an object in motion will continue at the same velocity in the absence of an external force.
In this experiment, the students will cause a collision between a cart carrying a mass and a piece of cardboard. The forces acting on the cart include the frictional force between its wheels and the floor, the gravitational force which keeps the cart on the floor, and at the point of collision, an external force from the cardboard. Because of this, the cart's velocity will decrease after impact. The forces acting on the mass include the frictional force between the mass and the cart, and the gravitational force. However, the mass will not incur an external force from the cardboard, as they do not come into direct contact. Therefore, the mass will continue with its original motion and move forward across the cart at impact.
When sandpaper is added to the cart surface, it greatly increases the frictional force between the mass and the cart. Upon collision, the mass should still move across the cart, but at a lower velocity because of the additional frictional force.
The concept of this experiment is similar to what happens during a car accident. If the passengers are not wearing seatbelts, they will continue to move forward at the same velocity until they incur an external force (the windshield). However, if seatbelts are worn (analogous to the tape the students will place on the mass in steps 8 and 14), the passengers will experience a force and will not move forward.
To print out the Student Copy only, click here.
Activity 1: Quarter Catch
*Practice this first to determine how many quarters you are comfortable using*
Activity 2: Rolling Cart and Inertia
To print out the Data Sheet only, click here.
1. Describe the forces acting upon the cart when it comes in contact with the cardboard. How does this explain its change in motion?
2. Describe the forces acting upon the mass at the point of collision. How does this explain its motion?
3. Did the addition of sandpaper to the cart affect your results? Why or why not?
4. Do your results follow Newton's First Law of Motion? Explain.
5. Do the results from this experiment demonstrate the importance of wearing a seatbelt inside a car?
Students with Special Needs
Some students may have difficulty manipulating some of the objects (especially in the Quarter Catch). These students could work with partners or in small groups.
Click here for further
information on laboratories with students with special needs.
Data sheet to be completed during the laboratory.