# Mass and Motion

In this unit, students encounter phenomena related to matter and energy as they learn about how engineers design materials with specific properties to address a wide range of societal needs.This page provides an overview of one lesson.

## Science Background for Teachers:

The science background gives teachers more detailed information on the phenomena students explore. Here is an excerpt from the science background section on mass and motion.

### Forces and Matter

The field of science that focuses on the relationship between the structure and properties of different materials is called materials science. Structure is the way in which parts are put together to form a whole. Materials scientists are interested in understanding the properties of existing materials, such as wool and cork, as well as in understanding how existing substances can be combined to form new materials with a specific set of properties that will allow them to be used in a particular way.

For example, the materials that make up the baseball, and the way that it is structured is very important because the ball experiences a tremendous amount of force during a game. The force applied by the batter isn’t the only force acting on the baseball. Forces are acting everywhere in the universe all the time. Even if you are standing still, you have many forces acting on you.

When you stand on Earth’s surface, gravity pulls you down toward the center of Earth. Gravity is the force of attraction between all matter. This means that gravity pulls objects together. It’s Earth’s gravity that keeps us and all objects on Earth from floating off into the atmosphere, and that pulls all objects thrown up in the air back to the ground. Gravity explains why all baseballs, no matter how hard they are hit, will eventually fall back to the ground.

The relationship between forces and motion was first described by a scientist called Sir Isaac Newton in the 1600s. Newton was fascinated by how things move. After much study, he realized that the motions of all objects follow the same three basic laws, which describe how forces cause objects to move.

### Newton’s 1st Law

All objects on Earth are pulled on by the force of gravity. Newton observed that when all of the forces acting on an object are balanced, the object will not change its motion.

When the forces acting on an object are equal, they are balanced. This is Newton’s first law of motion, and it describes inertia. Inertia is the tendency for an object at rest to remain at rest and an object in motion to remain in motion unless acted upon by an outside force. Simply put, objects tend to keep doing what they’re doing. Stationary objects won’t start moving, and moving objects won’t stop moving unless the forces pushing or pulling on these objects become unbalanced. Unbalanced forces occur when two opposing forces acting on an object are not equal.

Think of a baseball game. The baseball won’t begin to move on its own. It will only start moving when something acts on it, such as when a player picks it up or throws it. The force of a player throwing the ball or the bat hitting the ball provides the unbalanced force that causes the ball’s motion to change.

In the same way, once the baseball is in motion, it will stay in motion until the forces acting on it become unbalanced. When the ball is in the air, it eventually falls down because of unbalanced forces. For example, gravity pulls down on the ball, eventually causing it to fall back to the ground.

### Newton’s 2nd Law

Newton’s second law describes the relationship between the mass of an object, the magnitude of the force applied to it, and its resulting acceleration, or change in motion. This law can be written as an equation: “force = mass times acceleration.”

• Mass is the measure of the amount of matter that makes up an object or substance. It is measured in grams (g).
• Acceleration occurs whenever an unbalanced force acts on an object. It is the rate of change of an object’s velocity. (Velocity is the rate of change of an object’s position). Acceleration is measured in meters per second squared (m/s2).

Simply put, accelerations are changes in an object’s motion. Whenever an object speeds up, slows down, or changes direction, it accelerates. Speed is the rate at which an object covers distance in a period of time.

Newton’s second law says that when a force acts on an object and causes it to accelerate, its acceleration is directly proportional to the force and inversely proportional to its mass. Proportion is the relationship between things, as to size, quantity, or number.

In a directly proportional relationship, when one variable increases, the other variable increases. This means that the greater the force that is applied to an object of a given mass, the more the object will accelerate.

In an inversely proportional relationship, when one variable increases, the other decreases. The greater the mass of an object, the less it will accelerate when the same amount of force is applied.

### Newton’s 3rd Law

Newton’s third law is the action-reaction law. This law states that every force occurs as one member of an action-reaction pair of forces. Action-reaction pairs occur whenever two objects come into contact with each other. For every action, there is an equal and opposite reaction. In other words, the two forces point in opposite directions but have the same magnitudes.

You are experiencing action-reaction forces right now. Remember that gravity is constantly pulling down on you. In reaction to the force of gravity pulling down, the ground has its own force that pushes back up with the same amount of force. This keeps you from sinking into the ground.

If the ground did not push back with the same amount of force, you would fall into the ground. In this case, the forces would be unbalanced. Gravity would pull you down with a greater force that the force of the ground pushing back up.

A deflating balloon is another example of action-reaction forces. The push of the air escaping out the open end of the balloon is the action force. In reaction, the balloon moves in the opposite direction with an equal force.

Supports Grade 8

## Science Lesson: Understanding Mass and Motion

Students use the phenomenon of the mass of a baseball and its motion to analyze how objects transfer energy in a collision, tracing how energy changes from one form to another in an energy system and then exploring the relationship between an object’s mass and its speed.

## Science Big Ideas

• Forces are acting everywhere in the universe all the time. A force is any push or pull that acts on an object, changing its speed, direction, or shape.
• A stationary object still has forces acting on it. Because the object’s motion isn’t changing, the forces acting on it must be balanced.
• The motion of an object will only change when the forces acting on it become unbalanced.
• Whenever two objects come into contact with one another, they exert a force on each other (action-reaction forces), and that force transfers energy from one object to the other.
• Energy is the ability to do work. Work is any change in position, speed, or state of matter due to force.
• Forces transfer energy into or out of objects or systems. A system is a set of connected, interacting parts that form a more complex whole.

Discover Complete Hands-on Screens-off Core Science Curriculum for K-8 Classrooms

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## Science Essential Questions

• What forces are acting on you right now?
• When have you exerted a force on an object?
• What unbalanced forces would have to happen to cause an object to move?
• What are some examples from everyday life that provide evidence for the idea that a change in motion only occurs with an unbalanced force?
• How would a baseball in motion move if there were no forces acting on it?
• What energy transfer occurs when a pitcher throws the ball?
• What evidence is there that energy has transferred from the pitcher to the ball?
• How do we know that energy is transferred when two objects come into contact with one another, and that each object exerts an equal but opposite force on the other?

## Common Science Misconceptions

Misconception: Energy can be used up.

Fact: Just like mass, energy is always conserved. Energy transforms from one form to another, and can transfer into or out of objects or systems, but the total amount of energy is conserved.

## Science Vocabulary

Energy : the ability to do work

Force : a push or pull that acts on an object, changing its speed, direction, or shape

Kinetic energy : the energy of motion

Mass : the measure of the amount of matter that makes up an object or substance; measured in grams (g)

Potential energy : energy that is stored

Proportion :the relationship between things, as to size, quantity, or number

Speed: the rate at which an object covers distance in a period of time

System : a set of connected, interacting parts that form a more complex whole

Work : any change in position, speed, or state of matter due to force

## Lexile(R) Certified Non-Fiction Science Reading (Excerpt)

Forces and Energy

Forces are directly related to energy. Energy is the ability to do work. Work is any change in position, speed, or state of matter due to force. Examples of work include heating up an object or moving an object.

In other words, forces transfer energy into or out of objects or systems. A system is a set of connected, interacting parts that form a more complex whole.

To understand this relationship between energy, work, and force, it is first important to know that energy can be stored or in motion. Potential energy is energy that is stored. Kinetic energy is the energy of motion.

Forms of Energy

Energy of one kind can transform (change) into energy of another form in an energy system. Gravitational potential energy is the energy stored in an object as a result of its vertical position or height above the ground. For example, the higher a baseball is hit, the more gravitational energy it has. This is a cause-and-effect relationship. The height of the ball causes the amount of energy stored in the ball to change (the effect).

Transferring Energy

Any object that is moving has kinetic energy. A moving car and a running dog both have kinetic energy because they are in motion.

When a pitcher throws the ball, they apply a force to the ball that transfers kinetic energy to the ball. This transfer of kinetic energy is what powers the ball’s movement from the pitcher’s hand to the batter’s bat. When the batter swings, they generate their own kinetic energy. At the moment of contact between the ball and the bat, energy is transferred between the two objects.

Action-Reaction Forces

When the bat and the ball come into contact with one another, the ball exerts a force on the bat. The bat exerts the same amount of force on the ball.

We see evidence of this action- reaction pair in the change in motion of both the bat and the ball. Depending on how the batter hits the ball, the ball will change direction, moving away from the batter. The transfer of energy from the bat to the ball caused this change.

At the same time, the ball exerted a force on the bat that transferred energy. Evidence for this comes from the motion of the bat after contact. The bat might swing backwards a bit. If the force of contact is great enough, wooden bats have been known to splinter. This is because of the force exerted by the ball. All of these interactions occur because of Newton’s action-reaction law.

Energy Conservation

In a perfect system, the total amount of energy is conserved as it transforms from one form to another. This means that in a perfect system, the total amount of kinetic energy transferred from the pitcher to the ball would be the same amount of kinetic energy that the ball transferred to the baseball bat.

However, the real world is not a perfect system. Energy transfers out of the system at various points. For example, as soon as the ball leaves the pitcher’s hand, a force called drag occurs between the ball and the air. Drag, also called air resistance, is caused by air pushing against the baseball in motion. Drag occurs between a solid substance and a fluid such as air, and it slows motion because it causes some of the energy of the moving substances to change into heat. Drag transfers energy out of the system, causing the ball to slow down.

At the moment of contact between the bat and the ball, friction causes more energy to transfer out of the system. Friction is another force that slows motion when two objects rub against each other. Friction slows motion because it causes some of the energy of the moving object to change into heat.

Friction explains why a ball rolling on the ground slows down and eventually stops. According to Newton’s first law, the ball will continue moving unless the forces acting on it become unbalanced. In this case, friction is an unbalanced force that changes the ball’s motion.

At that same moment of contact, some of the energy is transferred out of the ball as it transforms to sound energy, which is energy produced by sound vibrations moving through a substance in waves. We hear evidence of this energy transfer in the loud crack made by the bat and the ball making contact.

Remember how the force of the contact distorts the baseball to half its original diameter? This is because the ball’s kinetic energy transforms to a form of potential energy called elastic energy, which is energy stored in objects when stretched. As the baseball’s shape is restored, the elastic potential energy transforms back to kinetic energy and the ball moves through the air.

## Hands-on Science Activity

In this lesson students investigate the phenomena of how the mass of a marble affects its average speed after a collision. They collect data from the experiment and look for patterns that might indicate a relationship between the mass of the marble and its resulting speed.

## Science Assessments

KnowAtom incorporates formative and summative assessments designed to make students thinking visible for deeper student-centered learning.

• Vocabulary Check
• Lab Checkpoints
• Concept Check Assessment
• Concept Map Assessment
• And More...

### See How KnowAtom Aligns to NGSS Science Standards

Discover hands-on screens-off core science curriculum for student centered K-8 classrooms. KnowAtom supports classrooms with all hands-on materials, curriculum, and professional development to support mastery of the standards.

### Supports Grade 8

#### Science Standards

Standards citation: NGSS Lead States. 2013. Next Generation Science Standards: For States, By States. Washington, DC: The National Academies Press. Neither WestEd nor the lead states and partners that developed the Next Generation Science Standards were involved in the production of this product, and do not endorse it.