Forces Georgia Performance Standards SPS8. Students will determine relationships among force, mass, and motion. b. Apply Newton’s three laws to everyday situations by explaining the following: Inertia Relationship between force, mass and acceleration Equal and opposite forces c. Relate falling objects to gravitational force d. Explain the difference in mass and weight.

Definition: A push or a pull Force What comes to mind? Definition: A push or a pull Gives energy to an object, sometimes causing it to start moving, stop moving or change direction.

Examples Magnet pulling iron Wind pushing a door Throwing a baseball What are some other examples http://www.bing.com/videos/search?q=funny+wind+videos&qs=n&form=QBVR&pq=funny+wind+videos&sc=0-0&sp=-1&sk=&adlt=strict#view=detail&mid=3D19DA049756328118E93D19DA049756328118E9

Total (Net) Force Acts in a particular direction Vector- shows magnitude and direction Force is a VECTOR. When 2 forces are exerted in the same direction, they ADD together. When 2 forces act in OPPOSITE directions, they combine by SUBTRACTION Force is measured in newtons. 1 Newton = 1 kg-m/s2

Balanced Forces forces that are in opposite directions and are equal in size. 40 N 40 N No change in motion, TOTAL (net) FORCE = 0 N Why? 60 N 60 N https://www.youtube.com/watch?v=yqi6LKt9ghk

Unbalanced Forces when TOTAL (net) force of an object is in 1 direction Movement is in which direction? 100 N 20 N 100 N Total (Resultant) Force? _________ 20 N Total (Resultant) Force? ______

Real life examples What are some other examples? https://www.youtube.com/watch?v=rDl0yF2HB98 What are some other examples? https://www.youtube.com/watch?v=6Vr7LaHEIcQ

Friction Is a Force that acts opposite to the motion. Causes a moving object to slow and/or stop. Rough surfaces have more friction than smooth surfaces What are some examples of friction?

4 Types of Friction Greatest Friction Static Friction– friction between objects that are NOT moving. Sliding Friction– friction between solid objects (at least one is moving) Rolling Friction– friction produced by moving wheels on a solid object Fluid Friction– force exerted by fluids (gases or liquids) (such as air, water or oil) Least Friction

Static Friction Examples…. The friction between these objects and the floor that you have to overcome to move them.

Sliding Friction Example… What are some other examples?

Rolling Friction Examples… What are some other examples?

Fluid Friction Examples… What are some other examples? https://www.youtube.com/watch?v=SLperYq2_98

Benefits of Friction Wheels to road in car allows car to stop. Brake system in car. Walking… shoes to ground. Causes Heat (in body) (shiver) Other Examples?

Problems with Friction Friction causes heat. (in machines) Lubricant (oil, wax or greases) – changes sliding friction to fluid friction. (lessening frictional force!!)

Newton’s 3 Laws of Motion 1st Law… aka Inertial Law A body in motion will stay in motion at a constant velocity unless acted upon by an outside force Inertia –the tendency of a body at rest to stay at rest or a body in motion to stay in motion http://www.youtube.com/watch?v=lbHt5mg_33w

2nd Law… (net) Force = mass X acceleration OR acceleration = (net) force / mass http://www.youtube.com/watch?v=0AK8yg5s2ps What if the Net force is zero? How much will a body accelerate? a = 0 N /500 kg So for a body to accelerate there must be a net force (however small)

3rd Law… For every action, there is an equal and opposite reaction Forces act in pairs * action/reaction law http://www.youtube.com/watch?v=D4j5bcaV2Ws&safe=active http://www.youtube.com/watch?v=Q_iYCg411BA http://www.youtube.com/watch?v=rkiPMzEeNCc&safe=active

Forces Any Questions?