Elementary Science

Science Focus LessonSC.5.P.13.1

Forces

Polk County Public Schools

SC. 5.P.13.1Benchmark: Identify familiar forces that

cause objects to move, such as pushes or pulls, including gravity acting on falling objects.

Essential Question:

How is the motion of an object affected by the forces acting upon the object?

Vocabulary:force magnetic forcegravity friction

A force is a push or a pull.Forces CHANGE motionForces cause objects to start moving, stop moving, change speed or direction.

What is a force?

Gravity is the force that attracts objects toward each other.

Gravity keeps Earth and planets in orbit around the sun

Gravity keeps the moon in orbit around the Earth

On Earth, gravity makes objects fall to the ground

Gravity

Gravity can act from a distance, it is NOT necessary for two objects to have contact with one another

Objects that have a greater mass produce a greater force of gravity

Objects that are closer to one another produce a greater force of gravity

All objects, regardless of mass, are pulled at the same rate of speed

Gravity has unique characteristics

Friction is a force between two surfaces rubbing against each other.

Friction is a force that works against the motion of an object.

Friction allows your bicycle to STOP when you apply the brakes

Friction prevents your feet from slipping when you are walking

Friction

Friction works only through direct contact-surfaces must rub against one another

Friction takes place between any type of matter: solid, liquid, or gas

Rough surfaces produce more friction than smooth surfaces

The greater the force pushing surfaces together, the greater the friction

Friction has unique characteristics

Magnetic force occurs between a magnet and matter that contains iron (or a few other magnetic materials)

The area around a magnet where the force of magnetism can be felt is called a magnetic field

Magnetic Force

Magnetic Force has unique characteristicsMagnetic force works at a distance As the distance between a magnet

and a magnetic object INCREASES the force of the magnetism DECREASES

All magnets have a north pole and a south pole

Opposite poles ATTRACT, or pull on, each other

Like poles REPEL, or push against, each other

Magnetism is strongest near the magnet’s poles

SummarizingIn your science notebook…

3- Name 3 forces

2- List 2 ways that a force can change motion

1- Define “ Force”

The motion of an object will change if it is pulled or pushed by something

Pulling or pushing applies a FORCE to an object

The amount of change in motion depends on the amount of force applied to it

The greater the force, the greater the change in motion

Forces change motion

The mass of an object affects the amount of force that is needed to change the motion of an object

More force must be applied to change the motion of a 120 kg football player than a 100 kg football player

Greater mass requires greater force

Gravity, friction, and other forces combine to change an object’s motion

A bowling ball moves down the alley when you apply a strong force, as it moves friction between the ball and the alley’s surface slows the ball down

A baseball moves because of the strong force of a bat, as it moves friction between the ball and the air slows it down, as it moves gravity pulls it to the ground

Forces work together

As gravity pulls an object to the ground the air around it slows it down.

Air is matter; there is friction when objects move through it

The more surface area an object has the more air resistance it will experience.

Air resistance works against gravitational force to slow thing down as they fall.

Air resistance is friction with air

Summarizing Answer the following question in

your science notebook: A baseball player hits a ball, it slows

as it flies through the air, it lands on the ground, rolls into the outfield, and then stops.

Explain what forces start the ball moving and cause the ball to slow down, fall down, and then stop.

1. A circus acrobat was shot out of a cannon. As she flew across the room, she began to fall down toward the net.What force caused the acrobat to fall down toward the net?

A. frictionB. heatC. gravityD. wind

Guided Practice

C is correct!!!

Gravity is the force that pulls objects to the Earth

2. A rolling ball will slow down until it finally stops. What force slows down and stops the ball?

A. gravityB. solar powerC. frictionD. speed

Friction is the force that slows objects down and causes them to eventually stop.

C is correct!!!

3. A soldier with a parachute jumped out of an airplane. After he opened his parachute, he fell more slowly.

What upward force slowed down his fall?

A. gravityB. magnetic forceC. air resistanceD. weight

Air resistance slowed down the fall of the soldier to the ground. Air resistance is friction with the air and works against gravitational force.

C is correct!!!

4. Mike lifted a heavy box. What force did he have to overcome to move the box upward?

A. gravityB. air resistanceC. frictionD. muscular

Gravity is the force that pulls objects to the ground, but it is also the force that holds objects, and us, to the ground.

A is correct!!!

SummarizingHow is the motion of an object

affected by the forces acting upon the object?

Answer this question using the following words.

gravityfriction

push or pullforce

magnetic force

Check Your Understanding1. William used a hammer to pound a nail

into a wooden board. When the nail was about halfway through the board, he stopped and turned the board upside down. The nail stayed in place in the board. Which of the following acts on the nail to keep it in place in the board?

A. Friction B. Gravity C. Magnetism D. Weight

Check Your Understanding 2. Jamesha has a bar magnet. What will happen when she brings the north end of her magnet to the south end of Brittany’s magnet? A. They will attract B. Nothing will happen C. They will repel D. Sparks will fly

Check Your Understanding3. A 10 kg, 15 kg, and 20 kg rock are rolling down a hill. Which rock will require the most force to stop?A. 10 kg rockB. 15 kg rockC. 20 kg rockD. All 3 rocks will require the same

force

Check Your Understanding4. The students in Mrs. Hoffman’s class

played tug-of-war. The girls pulled in one direction with a force of 150 N. The boys pulled in the opposite direction with a force of 100 N. Who won the game and why did they win?

A. The boys won because they applied a stronger force to the rope

B. The boys and the girls tied because they applied equal forces to the rope

C. The girls won because they applied a stronger force to the rope

D. Too much force was applied, the rope broke

Check Your Answers1. A. Friction2. A. They will attract3. C. 20 kg rock4. C The girls won

How do forces affect the motion of an object?

Summary Question