Inertia: An object in motion will tend to stay in motion
Summary
This activity is a take off of Galileo's experiment with the incline planes to show that an object in motion would in fact stay in a straight line motion if no outside forces acted were acting on it. Instead of using incline planes students will roll a ball on surfaces with different coefficients of friction (i.e. grass, cement, linoleum). As they decrease the friction of the surface, they will see the ball roll further each time. Then they can project what will happen on a surface with no friction. Will the ball eventually stop? Why or why not?
CollapseLearning Goals
1) Analyze the motion of an object and what eventually brings an object to rest.
2) Develop their understanding of friction whether the term "friction" is used or not.
3) Deduce the concept of inertia.
4) Analyze the flaws in the experiment (eg. It depends how hard you throw the ball.) and find possible ways to minimize error.
2) Develop their understanding of friction whether the term "friction" is used or not.
3) Deduce the concept of inertia.
4) Analyze the flaws in the experiment (eg. It depends how hard you throw the ball.) and find possible ways to minimize error.
Context for Use
Appropriate for an introductory freshman physical science class but can also be used for conceptual physics.
This is an ideal activity for those of us who do not have a large science budget.
Any class size is appropriate, the more space you have available the better (long hallways, extensive sidewalks). This hands on activity works well outside where large areas of different surfaces can be found such as grass, asphalt, cement.
This is an ideal activity for those of us who do not have a large science budget.
Any class size is appropriate, the more space you have available the better (long hallways, extensive sidewalks). This hands on activity works well outside where large areas of different surfaces can be found such as grass, asphalt, cement.
Description and Teaching Materials
That an object in motion will actually continue moving in a straight line forever unless some force acts on it can be a difficult concept for students to believe. When students discover this concept themselves with a simple hands on exercise they are more likely to believe the Law of Inertia.
Introduce this activity before introducing Newton's 1st Law of Motion. Have the students work in pairs. Each pair will need the following materials: a ball of any sort (although a ping pong ball may be too light), measuring tape and masking tape.
Have each pair find a starting point on one of the surfaces and mark it with masking tape. With as much consistency as possible roll the ball and mark and measure where the ball comes to rest. Make sure the ball does not hit a large impediment like a wall or large rock. Repeat for several trials and find the average displacement. Repeat on two or three more surfaces.
Compare surfaces and average displacements. What can be said about the surface and the displacement of the ball.
Many students will talk about friction. As a follow up to the lab talk about friction and what it is and how it works.
Propose a follow up question about a surface with no friction. What would happen to the ball? This is where they will deduce that an object in motion will continue in its motion if a force is not there to slow it down.
From the follow up question develop a scientific law to summarize the findings and the estimates of a simplified (i.e. frictionless) example.
Introduce this activity before introducing Newton's 1st Law of Motion. Have the students work in pairs. Each pair will need the following materials: a ball of any sort (although a ping pong ball may be too light), measuring tape and masking tape.
Have each pair find a starting point on one of the surfaces and mark it with masking tape. With as much consistency as possible roll the ball and mark and measure where the ball comes to rest. Make sure the ball does not hit a large impediment like a wall or large rock. Repeat for several trials and find the average displacement. Repeat on two or three more surfaces.
Compare surfaces and average displacements. What can be said about the surface and the displacement of the ball.
Many students will talk about friction. As a follow up to the lab talk about friction and what it is and how it works.
Propose a follow up question about a surface with no friction. What would happen to the ball? This is where they will deduce that an object in motion will continue in its motion if a force is not there to slow it down.
From the follow up question develop a scientific law to summarize the findings and the estimates of a simplified (i.e. frictionless) example.
Teaching Notes and Tips
I believe a lot of the students will talk about friction almost right away without thinking too much about their understanding of friction. This is a good time to explain that friction is a force that opposes motion.
Start with the surface with the least friction so that when they throw it without hitting a wall they consistently throw with that force for the following trials and surfaces.
Students should recognize that there will be error in the consistency of the throws but it is a good time to talk about acknowledging error and deciding if it is too significant to form a conclusion. My own experience has shown that two to a group allows for everyone to participate but too many balls rolling can make for an environment where student progress is hard to observe.
Start with the surface with the least friction so that when they throw it without hitting a wall they consistently throw with that force for the following trials and surfaces.
Students should recognize that there will be error in the consistency of the throws but it is a good time to talk about acknowledging error and deciding if it is too significant to form a conclusion. My own experience has shown that two to a group allows for everyone to participate but too many balls rolling can make for an environment where student progress is hard to observe.
Assessment
Lab report to be handed in along with a post lab discussion will help to determine if the students are achieving the goal of deducing part of Newton's Law of Inertia.
Standards
9-12.II.D.1—using Newton's laws
9-12.II.D.2—the effect of friction on an object's motion
9-12.II.D.2—the effect of friction on an object's motion