Physics in a bag is based on inquiry-based materials necessary to aid students in developing a better understanding of elementary physics. To internalize basic physics, students need to be aware of forces that influence motion of objects. Newton’s First and Second Laws of Motion are the focal points for this physics in a bag investigation, Forces and Motion, designed for grades 4-8.
This lesson is a hands-on, minds-on investigation that incorporates inquiry-based science strategies and techniques. Understanding scientific inquiry provides guidance in helping students understand this process of teaching and learning science.
Lesson Objectives
The first objective is for students to apply and understand Newton’s First Law of Motion. This law states that an object initially at rest is predicted to remain at rest if the total force on it is zero, and an object in motion remains in motion with the same velocity in the same direction. This law is based on balanced forces.
The second objective is for students to apply and understand Newton’s Second Law of Motion. This law states that the acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object. This law is based on unbalanced forces.
A third objective is for students to apply and understand force. A force is any push or pull upon an object resulting from the object's interaction with another object. Examples of forces are gravity and friction.
Investigation of Forces and Motion
Materials (per group)
- A plastic resealable bag large enough to hold all materials
- Straws
- Ten objects with different masses, shapes, and textures
- Metric ruler
- Textbooks
- Wooden block
- Coarse sandpaper
- Wax paper
- Scissors
- Heavy paper
- Markers, colored pencils, or crayons
- Paper clips
Procedures
Part One
- Students determine how many ways there are to make objects in their bags move using a straw. Additionally they need to develop a method for measuring force applied to objects to get them to move (for example, how many breaths it took to move an object 50 centimeters).
- Students identify what type of force (push or pull) they used to move each object.
- Students record their observations, including objects that could not move and why.
Part Two
- Students use textbooks to create an inclined plane.
- Students measure the distance a wooden block travels after it moves down the inclined plane.
- Students place sandpaper on the inclined plane and repeat Step 2.
- Students place wax paper on the inclined plane and repeat Step 2.
- Students record their observations in Steps 2, 3, and 4.
Part Three
- Students sit in their chairs, keeping their backs flat against the back of the chair. They cross their arms and hold them against their chest. Next they try to stand up without leaning in any direction.
- Students record their observations and explain why they were able to stand or why not.
Part Four
- Students cut out a balancing clown by folding the paper in half to ensure both sides are symmetric. Then they decorate the clown with their markers.
- Students place the clown on the tip of their finger to determine if it will balance.
- Next students add paper clips as weights to one side and record their observations.
- Allow students to add as many paper clips as want and to move them around, then record their observations.
Student Questions
- Which objects took the fewest and most breathes to move with the straw in part one?
- Which objects were your group unable to move in part one and why?
- What types of force were needed to get the objects to move in part one?
- On which surface did the wooden block travel in part two the greatest distance? Travel the least distance? Why?
- What force(s) acted on the wooden block?
- Why you able to stand keeping your back against the back of the chair in part three? Why or why not? What force(s) acted on your effort to stand?
- What force(s) caused the balancing clown to remain balanced or unbalanced in part four? Why?
- In which part(s) of this investigation where forces balanced or unbalanced? Why?
Additional questioning strategies are available at twenty questions to ask students in science projects.
Making Connections
This investigation provides students with the opportunity to develop an understanding of motion and the forces which act upon objects that balanced or unbalanced. For students to make important connections related to their observations and data, they need to write a science report regarding their observations, data analysis, and conclusions. Writing in science provides the best opportunity for students to internalize what they learned for future applications.
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