unit 5 lesson 4 forces copyright © houghton mifflin harcourt publishing company

Unit 5 Lesson 4 Forces

Copyright © Houghton Mifflin Harcourt Publishing Company


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.


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.

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.


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.



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.



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.



• 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.




• 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.




• What would happen to the girl’s direction if the dog at the bottom of the picture was very small?



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.



• 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.




• 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)




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.

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.


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.



unit 5 lesson 4 forces copyright © houghton mifflin harcourt publishing company

Documents

multiple forces

contact forces

unbalanced forces

magnetic forces

types of forces

individual forces

net force

smaller force