 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

 If your speed increases by 1 meter per second (m/s) for each second, then your acceleration is 1 m/s per second.
 Acceleration is the rate at which your speed (or velocity) changes.

 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 describes how quickly speed changes.
 Acceleration is the change in speed divided by the change in time.

Solving Problems
 A sailboat moves at 1 m/s.
 A strong wind increases its speed to 4 m/s in
3 s.
 Calculate acceleration.

Solving Problems
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

 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.

 There are three main ideas related to
Newton’s 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.

 Unbalanced forces cause changes in speed, direction, or both.

 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.

 The greater the mass, the smaller the acceleration for a given force.
 This means acceleration is inversely proportional to 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.

 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.

Solving Problems
 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:
 …car’s 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