Transcript Forces - pushes or pulls Contact forces

Forces - pushes or pulls
Contact forces - requires
contact to act.
Noncontact forces - action at a
distance.
Newton’s First Law objects resist
acceleration.
Law of inertia.
The mass of an object
is a quantitative
measure of inertia.
An inertial frame
of reference is
one in which
Newton’s law of
inertia is valid.
Newton’s second law F = ma.
The unit of force is the
Newton.
1 Newton =
2
1kg•m/s .
Free-body diagram
A diagram that
represents the object
and the forces that
act on it.
Ex. 1 - Two people are pushing a
stalled car. The mass of the car is
1850 kg. One person applies a
force of 275 N to the car, while the
other applies a force of 395 N. Both
forces act in the same direction.
Frictional forces of 560 N act in the
opposite direction. Find the
acceleration of the car.
Ex. 2 - A man is stranded on a raft
(mass of man and raft = 1300 kg). By
paddling, he causes an average force
P of 17 N to be applied to the raft in a
direction due east . The wind also
exerts a force A on the raft. This force
has a magnitude of 15 N and points
67° north of east. Ignoring water
resistance, find the x and y
components of the raft’s acceleration.
Ex. 3 - At the moment the forces
P and A begin acting on the raft,
the velocity of the raft is
0.15 m/s, in a direction due
east. Assuming that the forces
are maintained for 65 s, find the
x and y components of the raft’s
displacement during this time
interval.
Newton’s Third Law - for
every action (force) there
is an equal and opposite
reaction. The third law
describes two different
forces being applied to
two different objects.
Ex. 4 - The mass of a
spacecraft is mS = 11 000 kg
and that of an astronaut is
mA = 92 kg. The astronaut
exerts a force of F = +36 N on
the spacecraft from outside.
Find the accelerations of the
spacecraft and the astronaut.
Two general types of
forces:
Fundamental forces and
Nonfundamental forces.
Fundamental forces are
unique and are used to
describe other forces.
Three fundamental
forces:
1. Gravitational force
2. Strong nuclear force
3. Electroweak force.