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