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