This preview shows pages 1–4. Sign up to view the full content.
Newton’s laws:
(How to find
, from given forces?)
Newton #1. If the net force on an object is
zero,
is constant. (stay rest or keep
)
INERTIA (safety belt)
Objects want to keep doing what they are already doing
For example: in space ….
(Attention: If friction, Air resistance… net force
0)
Normal force N and gravity mg 2 forces on 1 object
N and mg are
2 balanced forces.
a
r
v
r
≠
v
r
Newton #2
If net force
0 .
is not constant,
a
0
object’s acceleration will be in the same
directions as the
net force.
≠
v
r
≠
a
m
F
net
r
r
=
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document SI Unit for forces : Newton (N)
F= m a
1 Newton force (net force), will give 1 kg object
1 m/s
2
acceleration. 1 N = 1 kg. 1 m/s
2
1 N = 1 kg.m/s
2
Example : gravity, ( free fall, jump, projectile,
same acceleration g. downward)
G= mg
weight = mass . g
g= 9.81 m/s
2
Also
g = 9.81 N/kg
= 9.81 N/kg =9.81 kg . m/s
2
kg
1 kg object’s weight on earth is 9.81 N
100gram (about 3 oz) object weights about 1 N.
Attention: when you solve problem, if you first
convert every value to standard SI unit.
(m, s, m/s, m/s
2
, N, ….) you can plug the numbers
and automatically get SI unit in your answer.
Strategy:
Always convert to SI unit before using equations.
Example:
=
=
−
=
minutes
1
.
0
/
24
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
This is the end of the preview. Sign up
to
access the rest of the document.
This note was uploaded on 08/25/2010 for the course PHYS 111 taught by Professor Jamesm.lockhart during the Spring '09 term at S.F. State.
 Spring '09
 JamesM.Lockhart
 Physics, Force, Inertia

Click to edit the document details