Transcript Section 2.2

Section 2.2
 Define and calculate
acceleration.
 acceleration
 Explain the
relationship between
force, mass, and
acceleration.
 Newton's second law
 Determine mass,
acceleration and force
given two of the
quantities.
 deceleration
Acceleration
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.
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.
Solving Problems
1. Looking for:
 …acceleration of sailboat
2. Given:
 …v1 = 1 m/s; v2 = 4 m/s; time = 3 s
3. Relationships:
 a = v2 – v1/t
4. Solution:
 a = (4 m/s – 1 m/s)/ 3 s
= 1 m/s2
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.
6.2 Newton’s second law
 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.
6.2 Newton’s 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.
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/s2