Section 2.2 Define and calculate acceleration. Explain the relationship between force, mass, and acceleration. Determine mass, acceleration and force given two of the quantities. acceleration deceleration Newton's second law Acceleration Acceleration is the rate at which your speed (or velocity) changes. If your speed increases by 1 meter per second (m/s) for each second, then your acceleration is 1 m/s per second. Acceleration Speed and acceleration are not the same thing. You can be moving (non-zero speed) and have no acceleration (think cruise control). You can also be accelerating and not moving! A falling object begins accelerating the instant it is released. Acceleration Acceleration describes how quickly speed changes. Acceleration is the change in speed divided by the change in time. ACCELERATION Solving Problems A sailboat moves at 1 m/s. A strong wind increases its speed to 4 m/s in 3 s. Calculate acceleration. 1.Looking for: acceleration of sailboat 2.Given: v 1 = 1 m/s; v 2 = 4 m/s; time = 3 s 3.Relationships: a = v 2 v 1 /t 4.Solution: a = (4 m/s 1 m/s)/ 3 s = 1 m/s 2 Solving Problems PRACTICE 1. A parachute on a racing dragster opens and changes the speed of the car from 85 m/sec to 45 m/sec in a period of 4.5 seconds. What is the acceleration of the dragster? 2. The cheetah, which is the fastest land mammal, can accelerate from 0.0 mi/hr to 70.0 mi/hr in 3.0 seconds. What is the acceleration of the cheetah? Give your answer in units of mph/sec. 3. The Lamborghini Diablo sports car can accelerate from 0.0 km/hr to 99.2 km/hr in 4.0 seconds. What is the acceleration of this car? Give your answer in units of kilometers per hour/sec. 4. Which has greater acceleration, the cheetah or the Lamborghini Diablo? (To figure this out, you must remember that there are 1.6 kilometers in 1 mile.) Be sure to show your calculations. Do Now: What is Newtons second Law? 6.2 Newtons second law There are three main ideas related to Newtons Second Law: 1.Acceleration is the result of unbalanced forces. 2.A larger force makes a proportionally larger acceleration. 3.Acceleration is inversely proportional to mass. 6.2 Newtons second law Unbalanced forces cause changes in speed, direction, or both. 6.2 Acceleration and force The second law says that acceleration is proportional to force. If force is increased or decreased, acceleration will be increased or decreased by the same factor. 6.2 Acceleration and mass The greater the mass, the smaller the acceleration for a given force. This means acceleration is inversely proportional to mass. 6.2 Acceleration, force and mass The acceleration caused by a force is proportional to force and inversely proportional to mass. The stronger the force on an object, the greater its acceleration. Force is directly proportional to acceleration. If twice the force is applied, the acceleration is twice as great. The greater the mass, the smaller the acceleration for a given force. Mass is inversely related to force. An object with twice the mass will have half the acceleration if the same force is applied. 6.2 Applying the second law Keep the following important ideas in mind: 1. The net force is what causes acceleration. 2. If there is no acceleration, the net force must be zero. 3. If there is acceleration, there must also be a net force. 4. The force unit of newtons is based on kilograms, meters, and seconds. A car has a mass of 1,000 kilograms. If a net force of 2,000 N is exerted on the car, what is its acceleration? 1.Looking for: cars acceleration 2.Given mass = 1,000 kg; net force = 2,000 N 3.Relationships: a = F / m 4.Solution: 2, 000 N 1,000 kg = 2 N/kg = 2 m/s 2 Solving Problems