Unit 7 Lesson 1 What Are Forces? Copyright © Houghton Mifflin Harcourt Publishing Company.

Unit 7 Lesson 1 What Are Forces?

Copyright © Houghton Mifflin Harcourt Publishing Company


Florida Benchmarks


• SC.5.P.13.1 Identify familiar forces that cause objects to move, such as pushes or pulls, including gravity acting on falling objects.

• SC.5.P.13.2 Investigate and describe that the greater the force applied to it, the greater the change in motion of a given object.


Florida Benchmarks


• SC.5.P.13.3 Investigate and describe that the more mass an object has, the less effect a given force will have on the object’s motion.

• SC.5.P.13.4 Investigate and explain that when a force is applied to an object but does not move, it is because another opposing force is being applied by something in the environment so that the forces are balanced.


Pushing and Pulling


• A force is a push or pull.

• Forces can change the movement of an object.

• Forces can change the shape of an object.


Pushing and Pulling


• Weight is a measure of the force gravity exerts on an object.

• Spring scales are used to measure force in units called newtons (N).

Two Common Forces


Gravity

• Gravity is a force of attraction between two objects. It acts even when objects are not touching.

• The size of the force increases as the mass of the objects increases.

• The size of the force decreases as the distance between the objects increases.


Friction

• Friction is a force that opposes motion.

• Friction acts between objects that are touching.

• Friction produces thermal energy.




Balanced or Unbalanced?


• Balanced forces are forces on an object that are equal in size and direction.

• Unbalanced forces are forces that cause a change in motion.

• A force must overcome the force of friction before an object will move.


Push (or Pull) Harder!


• Large forces can cause objects to change velocity, or accelerate, quickly.

• Changes in velocity include changes in speed and changes in direction.


Pull (or Push) Harder!


• What should the boy do differently to make the bell ring?


I’m Not Moving!


• If the same force is applied, objects with greater mass accelerate slower than objects with less mass.

• How can the steel ball be made to go higher?


I’m Not Moving!


• The larger the force applied to an object, the greater the acceleration is.

• The less an object’s mass is, the less force is needed to change its motion.


I’m Not Moving!


• Why does it take the full truck longer to stop than the empty truck?


Let’s Go to Mars!


• Unbalanced forces can allow rockets to oppose Earth’s gravity.

• Small booster rockets can change the direction of the vehicle’s motion.

• Rockets reach an “escape velocity” at which Earth’s gravity will no longer pull the vehicle back down.


Let’s Go to Mars!


• Balanced forces allow a spacecraft to move in one direction at a constant velocity through space.

• Once the spacecraft reaches Mars, it will accelerate toward the surface because of gravity.

Unit 7 Lesson 1 What Are Forces? Copyright © Houghton Mifflin Harcourt Publishing Company.

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