Flat Forces Review

Mass Most of the time the mass of the object will be given. Mass is inertia and inertia is mass! Mass is measured in kilograms (kg) If a mass is in grams (g) you have to convert it to kilograms (kg) Mass is not the same as Weight!

Weight Weight is also known as the Force Due To Gravity (Fg) Weight goes directly downward To find the weight use: Fg=mg Fg  Weight (N) m  Mass (kg) g  Acceleration due to gravity (on Earth 9.81 𝑚 𝑠 2 ) ( 𝑚 𝑠 2 ) Most of the time, the first step is to find Fg

Normal Force Weight is the force that is pulling you down, but normal force is the force pushing you back up. Normal Force is ALWAYS PERPENDICULAR TO THE SURFACE!!!! FN is measured in Newton's (N) FN = Fg on a flat surface

Flat Surface A surface can be rough, but still a flat surface Unless you are told/shown otherwise, the surface is flat On a flat surface, the Normal Force = Weight To find the Normal Force on a flat surface, you first have to find Weight If they give you a mass on a flat surface, you find weight by Fg=mg=FN

Friction Friction opposes the movement of the object (Fapp, Fpush, Fpull, etc.) Friction is measured in Newton's (N) Ff = µ F N Ff = Force of Friction (N) µ = Mu or Coefficient of Friction (No Units) F N = Normal Force (N) If they give you the mass of the object, you have to find the weight right away! Because Fg=FN If they give you two surfaces/materials, the Coefficient of Friction is in your reference table. It will be obvious because they will most likely only give you one given too. µ will never be more than 1. If you get an answer for µ that is over 1, go back and check your work. If you increase the µ, you increase the amount of friction.

Net Force Basics Net force is also known as Fnet Fnet is the sum of forces Fnet = ma Fnet = Net Force (N) m = mass (kg) a = acceleration of the object ( 𝑚 𝑠 2 ) ≠ g (9.81 𝑚 𝑠 2 ) Again… a IS NOT EQUAL TO g a is the acceleration of the object

Fnet Unbalanced If there is an unbalanced force (30N right & 10N Left), you have a Fnet (20N right) If you have an unbalanced force, you will have an acceleration. Why? Because every object has a mass. If you have a Fnet, then you MUST have an acceleration. Therefore, if you have an acceleration, you MUST have an FNet

Fnet Balanced If there is a balanced force (30N right & 30N Left), you have a no Fnet (0N) If you have a balanced force, you will have an acceleration of 0. Why? Because every object has a mass. If you have a Fnet of 0, then you MUST have an acceleration of 0. Fnet = ma Therefore, if you have an acceleration of 0, you MUST have an Fnet of 0

Fnet Graphs