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Week #2 Notes Monday, October 17th Reminder: Week #2 Vocabulary and notes are Due on Friday, October 21st Newton’s Second Law Fancy Definition: an object acted on by an unbalanced force will accelerate in the direction of the force Math Plug n Chug: Acceleration = Force / Mass Acceleration = m/s2 Force = Newtons Mass = kilograms Newton’s Second Law Easy Definition: If you apply a force, the object will move in the direction of the force Example: if you kick a ball forward….it will move forward. Draw it. Use it. Love it. Newton’s Second Law can tell you about changes in motion….using everyone’s favorite: math! Question: If a 10N force acts on a 2kg object, what acceleration does it give the object? Step #1: Write the plug n chug (formula) Step #2: Write the formula again, but replace with the actual measurements Step #3: Chug out the answer Which 2 numbers can you plug in? a = F/m a = 10N / 2kg a = 5 m/s2 Question: If a 10N force acts on a 2kg object, what acceleration does it give the object? Friction There are 3 kinds: Rolling, static, and sliding Rolling Friction When a wheel rolls over a surface The force is in the direction of the way the wheel is rolling Would I be able to ride my bike on ice as good as on concrete? Bike wheel is moving forward The rolling friction is forward Static Friction The friction that keeps a stationary object from moving Static Friction keeps her food in place http://www.inmagine.com/tt062/tt0132042-photo Why is her food not moving around on her tray? Sliding Friction Happens when 2 surfaces slide past one another Why is this player not moving in a straight line at a constant speed? Acceleration Change in velocity divided by the amount of time required for the change to occur If the object changes speed, direction, or both its accelerating Unit of measure: m/s2 If you calculate acceleration and the answer is positive: the object is speeding up If you calculate acceleration and the answer is negative: the object is slowing down Acceleration Acceleration = (final speed – start speed) time Calculate Acceleration When molecules collide with an object and slows its motion Example: hand out the car window Example: parachuting Example: walking in hurricane winds Air resistance is a type of friction ◦ Will be opposite of the direction of the object Air resistance increases with speed Air Resistance Weight & Mass They are not the same! Weight is the force of gravity on an object On Earth, objects fall back to Earth with the same acceleration: 9.8 m/s2 Weight = mass x acceleration due to gravity For us its 9.8 m/s2 Weight