Inertia, intro to vectors, FBD Tuesday, September 6, 2016

Unit 1: Static Forces Tuesday, 9/6 Respond to the following: What is acceleration? What causes an object to accelerate? Update your planner with the important dates below Upcoming important dates Monday, 9/12 – homework quiz Wednesday, 9/14 – unit quiz Friday, 9/16 – unit test

Simulating Inertia Newton’s First Law of Motion and Forces Materials: a pool ball and a level surface 1. Place the ball at rest on the level surface. a. What is needed to keep it at rest? b. What is needed to make the ball move? 2. Start the ball in motion in a straight line. a. What is needed to keep the ball moving in a straight line? b. What is needed to change the ball’s direction? c. What is needed to stop the ball? 4. What factors control how hard you have to push the ball to change its motion? 5. Write a statement which summarizes what you’ve learned.

Inertia Video guide questions Give an example of an object (football player) resisting change. What caused the object (football player)to change their motion? What is the most important factor effecting a players ability to resist change?

Law of Inertia Objects tend to stay at rest OR objects tend to stay in motion at a constant speed.

Matter Takes up space Atomic level; protons, neutrons, and electrons.

Objects Collection of particles The interactions of the particles are not important. Example; football player (scoring a touch down, homeostasis). Objects are treated as if they have no internal structures.

Properties of Objects We will consider different properties of objects throughout our Physics journey. For this unit we will focus on inertial mass. Inertial mass – causes objects to resist changes in motion; Measured In kilograms (kg); symbol - m

Systems A collection of objects which interact with each other Source: http://thesurge.com/stories/the-physics-of-car-crashes Source: http://www.newyorker.com/humor/daily-shouts/if-i-were-a-ballerina https://www.engadget.com/2015/09/13/solar-system-simulation-music/

Systems Are collections of objects interacting with one another. The properties of a system are determined by the properties of the objects and their arrangement (ex: consider the images from the previous slide). The observer determines which objects will be considered when analyzing a system (key component of analyzing AP Physics level questions)

Review: Vector v. Scalar Quantities Vector Quantity Fully described by both magnitude (number plus units) AND direction Represented by arrows -displacement -velocity -acceleration -force Scalar Quantity Fully described by magnitude alone -distance -mass -temperature -time -speed -electrical charge Intro idea with displacement v. distance demonstration. Pages 19-21 and 48-56

Vector Video https://www.youtube.com/watch?v=A05n32Bl0aY

Vector example Δx = 20 m North The bowling ball moved 20 meters north from the point of reference. Direction Δx = 20 m North Magnitude, scalar

Forces A Force is the action that occurs when objects interact with one another. Categories of forces Push Pull Think back to the football video; were there any pushes or pulls happening? Forces can change an objec’ts motion. Forces are vectors (magnitude and direction) Measured in Newtons (N) 1 N = Kg * m s2

Common Forces Familiarize yourself with the forces on the back of your handout.

Free body diagram (FBD) Pictorial representation of forces acting on an object.

Free body diagram steps Replace the object with a dot or box. Identify the force pairs acting on the object Identify contact forces acting on the object. Remember that only something that is physically touching the object can apply a contact force Possible types of contact forces – push, tension, normal, and friction Add arrows force and label the forces Add any force values that are known

FBD Example - static A block is sitting on a table.

FBD Example – constant velocity A block is being moved across a table.

Drawing FBD practice – 10 minutes

Net force equation

Net Force Example - static A block is sitting on a table.

Net Force Example – constant velocity A block is being moved across a table.

Weight vs. Mass Mass is matter (atomic level) Weight is the force of gravity acting on mass. Weight is represented by the symbol Fg Fg will always act on an object.

How to Calculate force of gravity (weight) Acceleration of gravity. On earth it is 9.8 m/s2. We Simplify and use 10.0 m/s2 Weight (force of gravity), measured in Newtons (N) Mass of the object, measured In kilograms (kg)

Example – calculating weight (Fg), A 1.5 kg block is sitting on a table

Example – calculating weight (Fg) A 1.5 kg block is moving across the table a a constant velocity on a table

Homework Take notes over the presentation in your notebooks Review, mark, and summarize vector notes.