Chapter 5 – Force and Acceleration Newton’s Second Law Chapter 5 – Force and Acceleration

Mass and Acceleration In Chapter 2 we learned that 𝑎𝑐𝑐𝑒𝑙𝑒𝑟𝑎𝑡𝑖𝑜𝑛= 𝑐ℎ𝑎𝑛𝑔𝑒 𝑖𝑛 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 𝑡𝑖𝑚𝑒 𝑖𝑛𝑡𝑒𝑟𝑣𝑎𝑙 Force causes acceleration; Newton observed that: The acceleration produced is directly proportional to the net force. For a given force the acceleration produced is inversely proportional to the mass. Combining those observations gives us 𝑎𝑐𝑐𝑒𝑙𝑒𝑟𝑎𝑡𝑖𝑜𝑛= 𝑛𝑒𝑡 𝑓𝑜𝑟𝑐𝑒 𝑚𝑎𝑠𝑠 or 𝑎= 𝐹 𝑚 Newton’s second law: The acceleration produced by a net force on an object is directly proportional to the magnitude of the net force, is in the same direction as the net force, and is inversely proportional to the mass of an object.

Free Fall and Air Resistance We’ve seen that objects in free fall all fall with an acceleration equal to g. But that’s true only if we can ignore air resistance. When the air resistance on a falling object equals its weight, the net force is zero and no further acceleration occurs. At that point the object has reached its terminal velocity. Felix Baumgartner skydive Altitude 39 km (24 mi) Reached an estimated terminal velocity of 1,357.64 km/h (843.6 mph), breaking the sound barrier

Free-Body Diagrams A free-body diagram is a diagram showing all the forces acting on an object. Free-Body Diagram Interactive

Force Exercises Force Interactive

Example Problem 1 Unfortunately for Vanessa, the wheels on her suitcase are not working. She pulls on the strap in an effort to budge it from rest and drag it to the curbside check-in desk. The free body diagram at the right depicts the forces acting upon the suitcase. Use force values to determine the net force, the mass and the acceleration of the suitcase. The values of the individual forces are: Fgrav = Fnorm = 207 N Ftens = 182 N Ffrict = 166 N

Example Problem 2 It's Friday night and Skyler has been assigned the noble task of baby-sitting Casey, his 2-year old brother. He puts a crash helmet on Casey, places him in the red wagon and takes him on a stroll through the neighborhood. As Skyler starts across the street, he exerts a 52 N forward force on the wagon. There is a 24 N resistance force and the wagon and Casey have a combined weight of 304 N. Construct a free body diagram depicting the types of forces acting upon the wagon. Then determine the net force, mass and acceleration of the wagon.

Example Problem 3 Moments after making the dreaded decision to jump out the door of the airplane, Darin's 82.5-kg body experiences 118 N of air resistance. Determine Darin's acceleration at this instant in time.