N3 law
N2 law
If the path between the fan
blades and shield is short,
we can make the assumption
The net forces acting on the cart
Shields up
1
3rd law Video
http://www.youtube.com/watch?v=PrJnWTcW55s
Clicker
You are an astronaut on a space walk when you discover that the jet pack no
longer works, leaving you stranded 25 feet from the spacecraft (relative
velocity =0). If the jet pack is removable, how you can still use it to return to
the ship.
A) You should push the jet pack away in the opposite direction from the spaceship
B) You should push the jet pack away toward the spaceship.
C) Removing the jetpack will allow you to float toward the spaceship
Normal Forces
The normal force is
the force exerted by a
surface on an object.
4
Normal Forces
The normal force may be equal to, greater than, or less than the weight.
5
Clicker
a) case 1
Below you see two cases: a man
pulling or pushing a sled with a
force F that is applied at an angle .
In which case is the normal force
greater for the sled?
b) case 2
c) it’s the same for both
d) depends on the magnitude of
the force F
e) depends on the ice surface
Case 1
Case 2
F denotes field force
F denotes contact force

F
 B
FAB+FEB +FEB = 0

F
 A  FBA+FEA = 0
Fij is the force exerted
by object i on object j
A
FAE
FBA
FEA
FAB
FBE
B
FEB
FEB
FBE
Earth

F
 A  FBA+FEA = 0
F denotes field force
F denotes contact force
Fij is the force exerted by
object i on object j
acceleration=0
FAE
A
FBA
FEA
FAB
FBE
FEB
FCB
B
FBC
FCB
FBC
Earth

F
 A  FBA+FEA = mAa
F denotes field force
F denotes contact force
Fij is the force exerted by
object i on object j
a
a
acceleration=a
FAE
A
FBA
FEA
FAB
FBE
FEB
FCB
B
FBC
FCB
FBC
Earth