Unit 5 Lesson 4 Forces Copyright © Houghton Mifflin Harcourt Publishing Company 1

Unit 5 Lesson 4 Forces Florida Benchmarks SC.6.N.3.3 Give several examples of scientific laws. SC.6.P.13.1 Investigate and describe types of forces including contact forces and forces acting at a distance, such as electrical, magnetic, and gravitational. Copyright © Houghton Mifflin Harcourt Publishing Company 2

Unit 5 Lesson 4 Forces Florida Benchmark SC.6.P.13.3 Investigate and describe that an unbalanced force acting on an object changes its speed, or direction of motion, or both. MA.6.A.3.6 Construct and analyze tables, graphs, and equations to describe linear functions and other simple relations using both common language and algebraic notation. Copyright © Houghton Mifflin Harcourt Publishing Company 3

Force of Nature What is a force? Unit 5 Lesson 4 Forces Force of Nature What is a force? In science, a force is a push or a pull. All forces are vectors. The unit that measures force is the newton (N). Forces do not always cause motion. Copyright © Houghton Mifflin Harcourt Publishing Company 4

Unit 5 Lesson 4 Forces How can forces act? Forces can act on objects that are in contact or on objects that are at a distance. Gravity is a force that pulls objects toward Earth. Magnetic forces can act at a distance or by contact. Copyright © Houghton Mifflin Harcourt Publishing Company 5

Unit 5 Lesson 4 Forces How can forces act? Forces can transfer energy from one object to another. Forces change an object’s motion by accelerating it unless the forces are balanced. Friction is force that occurs between objects that are touching. Friction causes objects to slow down. Copyright © Houghton Mifflin Harcourt Publishing Company 6

In the Balance How do multiple forces interact? Unit 5 Lesson 4 Forces In the Balance How do multiple forces interact? The net force is the combination of all the forces acting on an object. When forces act in the same direction, they are added to determine net force. When forces act in opposite directions, the smaller force is subtracted from the larger force. Copyright © Houghton Mifflin Harcourt Publishing Company 7

How do multiple forces interact? Unit 5 Lesson 4 Forces How do multiple forces interact? A net force of zero means the forces are balanced and will not cause a change in motion. Unbalanced forces produce a change in motion, or acceleration. Acceleration is always in the direction of the net force. Copyright © Houghton Mifflin Harcourt Publishing Company 8

How do multiple forces interact? Unit 5 Lesson 4 Forces How do multiple forces interact? Unbalanced forces are not always opposite. Net force will be in a direction that is a combination of the individual forces. When forces are not of equal strength, the direction will be closer to the direction of the stronger force. Copyright © Houghton Mifflin Harcourt Publishing Company 9

How do multiple forces interact? Unit 5 Lesson 4 Forces How do multiple forces interact? What would happen to the girl’s direction if the dog at the bottom of the picture was very small? Copyright © Houghton Mifflin Harcourt Publishing Company 10

Hitting the Brakes How do forces act on objects? Unit 5 Lesson 4 Forces Hitting the Brakes How do forces act on objects? Sir Isaac Newton described three laws of motion that explain the relationship between force and motion. Newton’s first law is that an object at rest remains at rest, and an object in motion maintains its velocity, unless it experiences an unbalanced force. Copyright © Houghton Mifflin Harcourt Publishing Company 11

How do forces act on objects? Unit 5 Lesson 4 Forces How do forces act on objects? An object will not start moving unless a push or pull acts on it. Objects in motion will continue to move unless a push or pull changes that motion. Newton’s first law is also called the law of inertia. Inertia is the tendency of all objects to resist any change in motion. Copyright © Houghton Mifflin Harcourt Publishing Company 12

How do forces act on objects? Unit 5 Lesson 4 Forces How do forces act on objects? Newton’s second Law is that the acceleration of an object depends on the mass of the object and the amount of force applied. force = mass × acceleration (F = ma) Copyright © Houghton Mifflin Harcourt Publishing Company 13

Unit 5 Lesson 4 Forces A Wearable Robot? Special powered suits are being developed by scientists that sense a person’s movement. Robotic suits can have air pumps that increase lifting force. Copyright © Houghton Mifflin Harcourt Publishing Company 14

A Matching Pair How do force pairs act? Unit 5 Lesson 4 Forces A Matching Pair How do force pairs act? Newton’s third law is that whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first. In other words, all forces act in pairs. Action and reaction forces are present even when there is no motion. Copyright © Houghton Mifflin Harcourt Publishing Company 15

Unit 5 Lesson 4 Forces How do force pairs act? Action and reaction forces in a pair do not act on the same object. The effects of action and reaction forces often are different. Multiple forces can act on an object at once. Copyright © Houghton Mifflin Harcourt Publishing Company 16