-Clean paper (2) / pencil -Friction/Gravity Notes WS Nov. 26, 2018 You need: -Clean paper (2) / pencil -Friction/Gravity Notes WS Nov. 26, 2018 Warm Up: Tell the difference in the motion of each car (based on the graph). Include a sketch of each graph. I CAN: identify balanced and unbalanced forces.

November 2018 Force/Motion Force/Motion Force/Motion Force/Motion

Energy Energy is what makes things move or change. What do you know? What do you think? Energy is what makes things move or change. PE KE 1. Ask students to share examples of energy and to explain what they think about it. Accept all answers without correction. 2. Hold a book a few feet above a table, as still as possible. Ask the class if the book has energy? Again, accept all answers. Drop the book and repeat the question. 3. Introduce a working definition of energy: “Energy is what makes things move or change.” Explain that we will explore energy during the next several activities. MECHANICAL ENERGY

How can we describe motion? Motion can be described by: DISTANCE (how far did it travel?) TIME (how long did it travel?) SPEED (how fast did it travel?) DIRECTION (which way did it go?) VELOCITY (speed + direction) ACCELERATION (does the motion change?)

No Motion

FAST vs. SLOW FAST SLOW

Starting & Stopping

Constant MOVEMENT Straight, not curved… Diagonal, not horizontal…

Speeding Up Slowing down

A FORCE is a PUSH or PULL in a particular DIRECTION. FORCES A FORCE is a PUSH or PULL in a particular DIRECTION.

FORCES FORCES AFFECT HOW OBJECTS MOVE. Forces can affect motion in the following ways: They can make objects: START MOVING MOVE FASTER MOVE SLOWER STOP MOVING CHANGE DIRECTION CHANGE SHAPE BIG SCIENCE IDEA

FORCES 1) Strength of the Forces 2) Direction of the Forces More than one force can act on an object at one time. What happens to the object when forces act depends on 2 things: 1) Strength of the Forces 2) Direction of the Forces

FORCES If the forces cancel each other out, and do not cause the object to move, the forces are said to be BALANCED. If the forces don’t cancel each other out – 1 force is stronger than the others – the forces are UNBALANCED and will cause a CHANGE IN MOTION.

Shoe lab Shoe on desk foam 60 grit sandpaper 220 grit sandpaper Item Force (pull) Force (push) Up Down 60 grit sandpaper 220 grit sandpaper foam Shoe on desk

Challenge The Grinch has stolen all the gifts of Who-ville. He knows that his “reindeer” can pull

FRICTION

The force that slows the ball to a stop is FRICTION. What will happen when the ball is released? When the ball reaches the bottom of the slope, will it keep moving forever? The force that slows the ball to a stop is FRICTION. Since the ball stops, there must be a force acting to slow the ball down.

What is Friction? Friction is a force that two surfaces exert on each other when they rub against each other. The direction of the friction force is always OPPOSITE to the direction of the motion. Direction of Motion Friction Force

Direction of Intended Movement Types of Friction Static Friction opposes the motion of an object that is at rest To make the object move, you have to exert a force larger than the force of static friction. Direction of Intended Movement Static Friction Force

Sliding Friction Force Types of Friction Sliding friction occurs when two solids slide over each other. Sliding friction makes car brakes work and stops athletes from slipping. Direction of Slide Sliding Friction Force

Types of Friction Rolling friction occurs when an object rolls across a surface. Rolling friction is easier to overcome than sliding friction for the same materials. Direction of Motion Friction Force

Types of Friction Fluid friction occurs when a solid object moves through a liquid or gas. Air resistance is a type of fluid friction. Direction of Motion Friction Force

Which type of friction is slowing down the object in each situation? You are slipping down a waterslide at Emerald Pointe. You use a lot of force to slide a desk across the floor. You’re riding a skateboard down the street and it slowly rolls to a stop. You try to push the couch, but can’t seem to move it. FLUID FRICTION SLIDING FRICTION ROLLING FRICTION STATIC FRICTION

Friction Thought Questions Why would you add oil to a rusty bike chain? Why would you add sand to an icy driveway or road? Why is it easier to move heavy furniture using a handcart rather than pushing it? Why would a shoe company be interested in studying friction? What would happen if we repeated the tug-of-war and one team had only socks on?

Review of Friction Forces

Review - What is Friction? Friction is a force that two surfaces exert on each other when they rub against each other. The direction of the friction force is always OPPOSITE to the direction of the motion. It SLOWS down moving objects! Direction of Motion Friction Force

Conclusions Questions Which surface material created the MOST frictional force? Which surface material created the LEAST frictional force? Give an example of a situation where we use a certain surface material to: a) REDUCE friction b) INCREASE friction

& AIR RESISTANCE The physics of falling GRAVITY & AIR RESISTANCE The physics of falling

The Force of Gravity Gravity is the force that pulls all objects down to the earth. Rain falls from the sky down to earth… If you drop a book, it falls to the ground… If you trip, you’ll fall down…

Universal Gravitation Actually in science, gravity is a force of attraction that acts between ALL objects (the earth, you, the desk, a book) The force of gravity is much STRONGER for LARGER objects (more mass).

Universal Gravitation Because the Earth is by far, the largest and closest object around, it has the greatest force of attraction... So, no matter where you are on earth, all things fall to the ground due to gravity…

What is “free fall”? When gravity is the ONLY force acting on an object, it is in free fall. In that case, gravity is an UNBALANCED FORCE which causes the object to accelerate.

(Spf – Spi) Acceleration = time D S T Math cheat sheet Formula Substitution Final answer with unit!

Acceleration due to Gravity Calculate the acceleration of an object in free fall. A = Final speed – initial speed time A = 50 m/s – 0 m/s 5 s Acceleration = 10 m/s2

Objects in Free Fall Do all objects fall at the same rate? If we dropped a bowling ball and a tennis ball from the same height, which would land first?

Question: How does mass affect the speed of a falling object? Mass and Gravity Nov. 15, 2017 Question: How does mass affect the speed of a falling object? Hypothesis: (What do you think will happen AND WHY?) Observations & Data Collection: Repeat each trial twice and record your observations. Ping pong ball vs. Wooden ball: Wooden ball vs. Metal ball: Ping pong ball vs. Metal ball: Conclusion: (One sentence)

Objects in Free Fall Do all objects fall at the same rate? ALL objects in free fall travel at the same rate, regardless of mass! In free fall, heavy objects and light objects fall at the same rate!

So, which will land first? WHY does the penny land first? Remember the force that opposes motion (slows things down)? FRICTION! Falling objects experience friction with the air called AIR RESISTANCE that slows them down.

Air Resistance The larger the object (more surface area), the more air resistance. That’s why parachutes work! The upward force of the air acting on the LARGE parachute slows you down as you fall.

Air Resistance Draw a diagram showing the forces… Gravity Draw a diagram showing the forces… Downward force of gravity is same on both. Upward force of air resistance is greater on the feather. The net force (down) is greater on the penny. Net Force on Penny Net Force on Feather

Without air resistance, all objects would fall at the same rate… Galileo Drops the Ball Hammer and Feather Drop on the Moon

That’s why astronauts weigh less on the moon! Gravity on the moon? The force of gravity is much weaker on the moon because… It is much farther away from earth. The moon is much smaller than earth. That’s why astronauts weigh less on the moon!

Gravity Review Gravity is the force that pulls all objects down to the earth. When gravity is the ONLY force acting, ALL objects accelerate at a rate of 10 m/s2. Mass doesn’t matter – in free fall, heavy objects and light objects fall at the same rate!

Air Resistance Review Some objects take longer to fall – they are slowed down by FRICTION with the air called AIR RESISTANCE. The larger the surface area, the greater the force of air resistance pushing up. Without air resistance, all objects would fall at the same rate…

Draw a free body diagram of the sky diver and label ALL the forces. Gravity = 1000 N Air Resistance = 800 N What is the net force? Air Resistance = 800 N Net Force = 200 N Gravity = 1000 N