Unit 3 Forces Introduction

Definition A force is a push or pull on an object. It’s an influence that can cause an object to be accelerated Measured in N (Newtons)

Types of Forces List as many types of forces you can: “THE FORCE” Buoyancy Magnetism Friction Static Electricity Gravity Elasticity Normal Force Tension

Veritasium Video clip: https://www.youtube.com/watch?v=GmlMV7bA0TM

How we draw Force Vectors Something that has both magnitude (how much) and direction (which way) Shown as an arrow Length is magnitude Point is direction Examples: 10N 5N

Free Body Diagrams A free body diagram is a way of showing all the forces acting on an object at the same time using vectors. Example: 10N 5N

Net Force Net force is the overall force acting on an object Examples:

Equilibrium Equilibrium is when the net force on something is ZERO. List objects in this room that are at equilibrium:

Normal Force A Normal Force is a force that is perpendicular to a flat surface. In a simple case such as an object resting upon a table… …the normal force on the object is equal to, but, in the opposite direction to the gravitational force applied on the object.

Normal Force What are the forces acting on you right now? Are you at equilibrium? How do you know? Normal Force is the upward force that ensures you don’t fall through the floor.

What Forces Are Acting on You Right Now? https://www.youtube.com/watch?v=aJc4DEkSq4I

Equilibrium in Motion Equilibrium is when ∑ F = 0 This could be when an object is at rest, or in constant motion that isn’t changing. Example:

Bill NYE! http://tune.pk/video/2761702/bill-nye-the-science-guy-motion-full-episode https://www.schooltube.com/video/c74a9a495e7544dba30a/bill%20nye%20-%20motion

Kajabe rules: https://www.youtube.com/watch?v=FBAr4W_eMjo

Four Way Tug of War: https://www.youtube.com/watch?v=-Cefl3S_L-w Kajabi Can-Can finals: https://www.youtube.com/watch?v=rfNEIwCBZw8

Intro to Newton’s Second Law Acceleration and Force

Refresher:  

Force Causes Acceleration Any object that accelerates is acted on by a push or a pull (a force!) Acceleration depends on the net force Examples: As net force increases, acceleration increases As net force decreases, acceleration decreases

Mass is a Measure of Inertia The greater the mass, the greater the force needed for a given acceleration. The greater the mass, the greater its inertia Examples:

What mass isn’t… Mass is not volume Examples: Mass is not weight

Mass Resists Acceleration  

Newton’s 2nd Law  

Free Fall Objects in free fall have equal acceleration Free fall is falling only under the influence of gravity, where other forces such as air drag can be neglected. Example: Textbook and paper demo

Terminal Velocity In free fall, weight pulls down The force of air resistance (Fair) pushes up When they equal each other, the Σ F = 0 This means there is no acceleration Does it stop? No, just has constant v…( Δv = 0 ) Terminal Velocity is when there is no more acceleration due to the force of air resistance (Fair) = Force of gravity (Fg).

Terminal Velocity video #1 https://www.youtube.com/watch?v=EabUUrZFnFE

Terminal Velocity questions For the video you just watched, draw a free body diagram for each of these times: (think about if the forces are equal or not) In the plane, before jumping After jumping before reaching terminal velocity (TV) Once TV is reached After opening parachute, before new TV is reached After reaching new TV Right when hitting the ground (for just a split second) Once on the ground holding still

Terminal Velocity questions Look at the free body diagrams you just drew. Circle those that show the skydiver accelerating. How did you decide this?

Terminal Velocity video #2 https://www.youtube.com/watch?v=lBk62CWsGok Enjoy 