Back To Course

Physics 111: Physics I16 chapters | 140 lessons | 11 flashcard sets

Are you a student or a teacher?

Try Study.com, risk-free

As a member, you'll also get unlimited access to over 75,000 lessons in math, English, science, history, and more. Plus, get practice tests, quizzes, and personalized coaching to help you succeed.

Try it risk-freeWhat teachers are saying about Study.com

Already registered? Log in here for access

Your next lesson will play in
10 seconds

Lesson Transcript

Instructor:
*Amanda Robb*

In this lesson we'll be learning how to use graphical representations of forces, like free body diagrams and force vs acceleration graphs, to explain Newton's second law. By the end of the lesson, you'll understand these diagrams and how to calculate the net force in two dimensions.

Picture an object in motion. It could be a skydiver jumping out of an airplane or a rocket zooming out into space. But even smaller objects experience motion, like a mouse skittering across the floor. What's common between all these examples?

They're all in motion, and they're all **accelerating**, or experiencing a change in velocity. Although velocity can stay constant, most moving objects we experience in the real world accelerate. But, how can we predict how an accelerating mass will move? Scientists use a revelation from hundreds of years ago in the 1600s, known as Newton's second law, to answer this question.

**Newton's second law** says that mass multiplied by acceleration is equal to the force acting on an object, or:

*F=ma*

where *F* is force, *m* is mass, and *a* is acceleration.

In all the real world examples we mentioned previously, there is more than just one force acting on an object. In order to decide how the object will move, we need to consider how the forces will combine first. To do this, we can use a handy tool called a **free body diagram** to show which forces are acting on an object.

Objects take all types of forms, and since we're not all artists, we can keep it simple by representing the object as a dot in the diagram. Then, all forces extend out from the dot using arrows. Some forces will push the object forward, such as the applied force (or *F**app*) when an object is pushed. Other forces include tension (or *F**T*) when an object is pulled or hung by a string, and force due to friction (or *F**f*) which opposes the applied force.

Every object has force due to gravity (or Fg) pushing down on it as long as it is on Earth. Objects that are on a surface also have a force that opposes gravity called the normal force (or *F**N*). It extends perpendicular from the surface the object rests on and is the same value as the force due to gravity as long as it is on a flat surface and not an incline.

Let's look at an example: this free body diagram below. A toy car travels across a table with an applied force of 10N. Friction on the table opposes this force with 2N. The car experiences a force due to gravity of 1N.

Since the object is on a flat surface, we can assume that the normal force is equal to the force due to gravity.

Now that we have this free body diagram, what do we do with it? Next, in order to see how motion changes for the object, we must calculate the **net force**. The net force is the sum of forces extending in one plane of motion. You add forces going forward and subtract forces going backward in the horizontal plane. Forces going up in the vertical plane are added, and forces going down are subtracted. You can't add horizontal forces to vertical forces; we will have two separate quantities for net force on this object.

Let's look at our example.

Since the toy car moves forward with 10N, we will add this force. The frictional force moves backward, so we subtract 2N. Our net force in the horizontal plane is 8N.

In the vertical plane, the forces balance each other, 1N - 1N = 0N. So, there is no net force acting on the object in the vertical plane.

The forces in the horizontal plane for our toy car are **unbalanced**. This means that the opposing forces don't equal each other, and the object will move forward with 8N. The forces in the vertical plane are balanced, so the object will continue with its current course of motion in the vertical plane, which is to stay still.

But, now how do we determine how much the object will accelerate? Let's say we know the car's mass: 4kg. Now, we can apply Newton's second law, which says *F=ma*.

Our force is 8N, and our mass is 4kg, so we get:

8N = 4kg * *a*

*a* = 8N / 4kg

*a* = 2m/s2

So, now we know that our toy car will accelerate at 2m/s2 across the table with these forces applied.

Like other formulas in physics, we can also use graphs to assess the relationship between variables. Let's look at an example experiment.

Let's pretend you have a block with an unknown mass. You apply a specific acceleration to the box and measure the force needed using a spring scale. Now, you can make a graph with acceleration as the independent variable and force as the dependent variable.

Recall the equation for slope, change in *y* divided by change in *x*. When we add in the variables from the graph, we get *F/a*, which based on Newton's second law is equal to mass. So, the slope of our force versus acceleration graph should be equal to the mass of the object.

**Newton's second law** states that force is equal to mass multiplied by acceleration. **Acceleration** is any change in an object's velocity. The formula for Newton's second law is:

*F=ma*

where *F* is force, *m* is mass, and *a* is acceleration.

Like other formulas, this formula can be adjusted, depending on which variables you know and which you don't. To apply this law, you must first calculate the **net force** acting on an object by adding together all of the forces in one plane of motion. Forces can be identified using a **free body diagram** that shows all the forces acting on an object. After calculating net force, you can determine if the forces are balanced or **unbalanced**, in which there will be a change in motion. Then, you can use Newton's second law with net force to calculate acceleration. Mass can be found by calculating the slope on a force versus acceleration graph.

To unlock this lesson you must be a Study.com Member.

Create your account

Are you a student or a teacher?

Already a member? Log In

BackWhat teachers are saying about Study.com

Already registered? Log in here for access

Did you know… We have over 160 college courses that prepare you to earn credit by exam that is accepted by over 1,500 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Not sure what college you want to attend yet? Study.com has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

You are viewing lesson
Lesson
7 in chapter 6 of the course:

Back To Course

Physics 111: Physics I16 chapters | 140 lessons | 11 flashcard sets

- Newton's First Law of Motion: Examples of the Effect of Force on Motion 8:25
- Force: Definition and Types 7:02
- Mass and Weight: Differences and Calculations 5:44
- What is Friction? - Definition, Formula & Forces 8:44
- How to Use Free-Body Diagrams to Solve Motion Problems 6:58
- Inclined Planes in Physics: Definition, Facts, and Examples 6:56
- Newton's Second Law: Meaning & Calculations 5:58
- Practice Applying Newton's Second Law 5:46
- Practice Applying Force & Acceleration Formulas 7:03
- Newton's Third Law of Motion: Examples of the Relationship Between Two Forces 4:24
- Practice Applying Newton's Third Law 5:19
- Go to Basics of Newton's Laws of Motion

- SIE Exam Study Guide
- Indiana Real Estate Broker Exam Study Guide
- Grammar & Sentence Structure Lesson Plans
- Foundations of Science Lesson Plans
- Career, Life, & Technical Skills Lesson Plans
- Business Costs, Taxes & Inventory Valuations
- Using Math for Financial Analysis
- Assessments in Health Education Programs
- Governmental Health Regulations
- Understanding Health Education Programs
- AFOQT Prep Product Comparison
- ACT Prep Product Comparison
- CGAP Prep Product Comparison
- CPCE Prep Product Comparison
- CCXP Prep Product Comparison
- CNE Prep Product Comparison
- IAAP CAP Prep Product Comparison

- What is Defamation of Character? - Definition & Examples
- Regionalism in Politics: Definition, Characteristics & Types
- Latitude & Longitude Lesson for Kids: Definition, Examples & Facts
- Teaching Methods: Types & Strategies
- The Crow and the Pitcher Activities
- The Albertosaurus Mystery Activities
- Holocaust Discussion Questions for High School
- Quiz & Worksheet - Factors that Affect Gas Exchange in People
- Quiz & Worksheet - Dally's Death in The Outsiders
- Quiz & Worksheet - What is Aqua Regia?
- Quiz & Worksheet - Christopher Columbus's Voyages
- Analytical & Non-Euclidean Geometry Flashcards
- Flashcards - Measurement & Experimental Design
- Bullying in Schools | Types & Effects of Bullying
- Digital Citizenship | Curriculum, Lessons and Lesson Plans

- WEST Middle Level Humanities (Subtests 1 & 2)(052/053): Practice & Study Guide
- Illinois AQB Certified General Appraiser Exam: Study Guide
- WEST English Language Arts (301): Practice & Study Guide
- Accuplacer Reading Placement Test Study Guide
- PSSA - Science Grade 8: Test Prep & Practice
- Fluency & Reading Development
- Coaching & Feedback in Management
- Quiz & Worksheet - Simplifying a Division Expression
- Quiz & Worksheet - Stereotype Threat Theories
- Quiz & Worksheet - Free Association
- Quiz & Worksheet - Common Industrial & Laboratory Acids
- Quiz & Worksheet - Curriculum Development Models & Processes

- What is Torque? - Definition, Equation & Calculation
- Kinesiological Analysis: Description & Major Components
- List of Standardized Tests
- What to Study for a Citizenship Test
- Study.com's GED Program for Enterprise
- How to Calculate College GPA
- SAT Test Locations & Dates
- Journal Writing Prompts
- CHPN Certification Requirements
- Do Private Schools Take Standardized Tests?
- How to Pass a Writing Test
- Creative Nonfiction Writing Prompts

- Tech and Engineering - Videos
- Tech and Engineering - Quizzes
- Tech and Engineering - Questions & Answers

Browse by subject