Science Focus Lesson SC.5.P.13.1 Forces Elementary Science Science Focus Lesson SC.5.P.13.1 Forces Benchmark Clarifications Students will identify familiar forces that affect how objects move. Students will identify scenarios whereby gravity is overcome. Students will identify and/or describe examples of magnetic attraction and repulsion. Content Limits Items assessing familiar forces are limited to pushes, pulls, friction, gravity, and magnetic force. Items may only require the interpretation of two forces at a time. Items referring to friction will only assess the force of friction as a resistance to movement. Items that assess magnetic attraction will not use the context of separating mixtures and solutions. Polk County Public Schools

SC. 5.P.13.1 Benchmark: 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 force gravity friction Force- a push or a pull Gravity-a natural force that pulls objects towards each other Magnetic force- a force that pulls magnetic materials across a distance Friction- a force between two surfaces rubbing against each other. Friction works against the motion of an object.

What is a force? A force is a push or a pull. Forces CHANGE motion Forces cause objects to start moving, stop moving, change speed or direction. A push or a pull is necessary to start an object in motion.

Gravity 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 All objects attract each other.

Gravity has unique characteristics 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 Different planets in the solar system have different masses. Because of this the force of gravity on each planet is different. Weight is the measure of the pull of gravity on an object. Air has mass. The pull of Earth’s gravity on air gives air weight. That weight is greatest at the Earth’s surface because there is much air pushing down from above. Earth’s gravity pulls on water producing water pressure which increases at greater depths. YES…it’s true…unless there is a opposing force like air resistance, ALL OBJECTS FALL AT THE SAME RATE OF SPEED. So…drop a book and a pencil and they will hit the ground at the same time.

Friction 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 causes a ball to stop rolling, brakes of a bike or car to work, etc.

Friction has unique characteristics 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 A parachute works against gravitational force because there is friction between the parachute and the air A baseball slows down because there is friction between the baseball and the air (it falls to the ground because of the gravitational force) A meteor is a streak of light produced when a space rock plunges through Earth’s atmosphere. The rock rubs against the air which produces friction. The friction produces heat that burns up the rock

Magnetic Force 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 has unique characteristics Magnetic 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 The Earth acts as it if had a bar magnet pushed through the center from north to south. One end is called the north magnetic pole, the other is called the south magnetic pole. A compass needle lines up with Earth’s magnetic poles. The geographic North and South Poles are points at the ends of Earth’s axis. The magnetic poles and the geographic poles are not in exactly the same place.

Summarizing In your science notebook… 3- Name 3 forces 2- List 2 ways that a force can change motion 1- Define “ Force” 3- Gravity, Friction, Magnetic Force 2- Stop/Start/Go Faster/ Go Slower/ Change Direction 1- A force is a push or a pull

Forces change motion 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

Greater mass requires greater force 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

Forces work together 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

Air resistance is friction with air 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.

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. Hitting the ball with the bat is a force (push) that puts the ball in motion. Air resistance and gravity causes the ball to slow and fall to the ground. Friction between the ball and the grass causes the ball to stop rolling. Discuss student summaries to ensure they recognize all forces at work.

Guided Practice 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. friction B. heat C. gravity D. wind

C is correct!!! Gravity is the force that pulls objects to the Earth

2. A rolling ball will slow down until it finally stops 2. A rolling ball will slow down until it finally stops. What force slows down and stops the ball? A. gravity B. solar power C. friction D. speed

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

What upward force slowed down his fall? 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. gravity B. magnetic force C. air resistance D. weight

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

A. gravity B. air resistance C. friction D. muscular 4. Mike lifted a heavy box. What force did he have to overcome to move the box upward? A. gravity B. air resistance C. friction D. muscular

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

Summarizing force friction gravity magnetic force push or pull How is the motion of an object affected by the forces acting upon the object? Answer this question using the following words. friction gravity Possible response: A force is a push or pull that is need to start objects moving. Gravity is a force that pulls objects to the ground. Once objects are moving they can be slowed down or stopped by friction. A magnetic force is when a magnetized piece of either iron, steel, nickel or cobalt comes close to a magnet. magnetic force push or pull force

Check Your Understanding 1. 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 Understanding 3. A 10 kg, 15 kg, and 20 kg rock are rolling down a hill. Which rock will require the most force to stop? 10 kg rock 15 kg rock 20 kg rock All 3 rocks will require the same force

Check Your Understanding 4. 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? The boys won because they applied a stronger force to the rope The boys and the girls tied because they applied equal forces to the rope The girls won because they applied a stronger force to the rope Too much force was applied, the rope broke

Check Your Answers A. Friction A. They will attract C. 20 kg rock C The girls won When the board is turned upside down, the nail will only stay in place if the forces are balanced. Gravity is pulling the nail down, and friction is acting in the opposite direction. Opposites attract The greater the mass, the greater the force needed to change motion The girls applied a greater force

Summary Question How do forces affect the motion of an object?