## Forces and Motion and their Relationships

The teacher understands forces and motion and their relationships.

This competency has several subthemes that contribute to overall understanding of forces and how they affect motion of objects. For a general introduction to the topic, watch this video from BioEd Online, in which Dr. Greg Vogt uses rockets to illustrate Newton's famous three laws of motion. Each law is a statement describing how force affects the motion of objects.

### Properties of Universal Forces

The beginning teacher demonstrates an understanding of properties of universal forces (e.g., gravitational, electrical, magnetic).

#### Key Concepts

• A force is any influence that causes an object to undergo a change in speed, a change in direction, or a change in shape. Force also can be thought of as a push or a pull.
• There are four fundamental forces, sometimes referred to as universal forces. They are, in order of increasing strength: gravitational force, weak nuclear force, electromagnetic force, and strong nuclear force.

#### Resources

Fundamental Forces. The Department of Physics and Astronomy at Georgia State University describe the four fundamental forces and their relative properties in their HyperPhysics site.

Gravitational Force. Professor Walter Lewin explains Newton's Law of gravitation in this video from the Massachusetts Institute of Technology.

Weak Force. Weak nuclear forces are responsible for radioactivity. Project SLAC at Stanford University explains these weak forces in the introduction to a lesson.

Electromagnetic Force. Electromagnetism is a powerful force that extends throughout the universe and is fundamental to living things, machines, electronics, etc. Professor Walter Lewin explains electromagnetic force and its many applications in his lecture, "The Importance of Electricity and Magnetism."

Strong Force. The strong force binds protons and electrons in the nucleus of the atom. A description of the strong force, one of the four basic forces in nature, is found on the InnovateUS website.

There are four fundamental forces, sometimes referred to as universal forces. They are, in order of increasing strength: gravitational force, weak nuclear force, electromagnetic force, and strong nuclear force.

### Measuring, Graphing and Describing Changes in Motion

The beginning teacher understands how to measure, graph and describe changes in motion using concepts of displacement, speed, velocity and acceleration.

#### Key Concepts

• Displacement, in relation to motion, is an object's overall change in position.
• Speed is a scalar quantity and is the rate of change of an object's position. It is the distance traveled divided by time.
• Velocity is a vector quantity that includes both speed and direction of motion.
• Acceleration is the rate of change of an object's velocity with time. Since velocity is a vector quantity, acceleration occurs when a direction is changed even though the speed remains constant.
• Graphs can be used to illustrate motion.
• The term, "rate," refers to a ratio between two measurements. When talking about movement, rate usually describes units of distance per unit of time. For example, miles per hour, or meters per second.

#### Resources

Displacement. Displacement vs. distance is illustrated and explained with practical examples by The Physics Classroom.

Graphing Motion. Graphing different measures of motion is explained in the "Graphs of Motion" page of the Physics Hypertextbook.

Scalars and Vectors. Use Lesson 1 of this Physics Classroom Chapter to learn the difference between scalar and vector quantities of force and motion, and how to describe motion through graphs and equations. Continue on to Lessons 2, 3 and 4 to learn more about graphing the position of an object over time.

### Vector Nature of Force

The beginning teacher understands the vector nature of force.

#### Key Concepts

• A vector quantity describes both the magnitude of a force and its direction.

#### Resources

Vectors and Scalars. Watch this video from Khan Academy for a description and explanation of vectors and scalars.

Vectors. This Physics Classroom lesson on Vectors, Motion and Forces details the nature of vectors under a variety of situations with descriptions, illustrations, animations and short quizzes.

### Newton's Laws to Describe the Motion of an Object

The beginning teacher identifies forces acting on an object and applies Newton's laws to describe the motion of an object.

#### Key Concepts

• A force is any influence that causes an object to undergo a change in speed, a change in direction, or a change in shape. Force also can be thought of as a push or a pull.
• When an object is traveling in a straight line at a constant speed, no force is acting on it.
• When an object is traveling on a curved line or its speed is changing, an unbalanced force is acting upon it.

#### Resources

Newton's Laws. Information on Newton's laws of motion can be found in the NASA Rockets Educator Guide chapter, "How Rockets Work" (PDF).

Newton's Laws with Examples. The Physics Classroom chapter, "Newton's Laws," uses specific examples to describe and analyze Newton's three laws of motion. Work through each lesson to boost your understanding.

### Examples of the Relationship between Force and Motion

The beginning teacher analyzes the relationship between force and motion in a variety of situations (e.g., simple machines, blood flow, geologic processes).

#### Key Concepts

• A force is any influence that cause an object to undergo a change in speed, a change in direction, or a change in shape. Force can also be thought of as a push or a pull.

#### Resources

Vectors and Scalars. Watch this video from Khan Academy for a description and explanation of vectors and scalars.

Newton's Laws with Examples. The Physics Classroom chapter, "Newton's Laws," uses specific examples to describe and analyze Newton's three laws of motion. Work through each lesson to boost your understanding.

Levers. With a focus on mechanics and exercise, ExRX.net illustrates and analyzes the relationship between Newton's laws and levers is illustrated and analyzed.

Simple Machines. This chapter, from a basic mechanics course created at Rice University, uses graphics and mathematics to explain simple machines.

Geologic Processes. Internal forces cause Earth's tectonic plates to move in relation to each other. Tectonic-forces.org provides a detailed explanation of tectonic forces.

Blood Flow. Blood flows through the body due to forces caused by muscle contractions. How Stuff Works explains the "mechanism" of human blood flow.