Mass and Acceleration. Types of Forces Noncontact ForcesContact Forces GravitationalNuclear...
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Mass and Acceleration
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Newton’s 1 st Law: No net force - no acceleration No acceleration = constant velocity
Transcript of Mass and Acceleration. Types of Forces Noncontact ForcesContact Forces GravitationalNuclear...
Mass and Acceleration
Types of Forces
Noncontact Forces Contact Forces
Gravitational Nuclear Pushes Pulls
Electric Magnetic Friction Normal
Tension
W
M
T
N fperpendicular to
surface
Electromagnetic
Newton’s 1st Law: No net force - no acceleration
No acceleration = constant velocity
Motion of the Block
at rest
uniform motion to the right
moves to the right and speeds up without changing direction
moves to the right, slows down and stops without changing direction
Velocity Acceleration Push or Pull Necessary to Maintain Motion
Dry Ice on Slate
0 0 0
0 0
Pretest #3(“the crate in the snow”)
Fby gravity
Fby snow
?
Pretest #3(“the crate in the snow”)
Fby gravity
Fby snow
Newton’s 2nd Law: Net force causes acceleration (not velocity) The net force is the vector sum of all the individual forces
on an object.
WE,b
Nr,b
Nr,b
Fnet
WE,b
a
Acceleration is in same direction as the net force.
a
Types of Forces
Noncontact Forces Contact Forces
Gravitational Nuclear Pushes Pulls
Electric Magnetic Friction Normal
Tension
W
M
T
N f
Electromagnetic
Which one is the net force?
What’s the mass? A measure of “how much stuff”
A measure of how hard it is to speed up or slow down
Very different than weight!
Hammer of Death
More net force - more acceleration(constant mass)
F
a
F
a
a Fnet
More mass - less acceleration(constant net force)
F
a
a
F
a M1
Putting it all together
a MFnet
Constant ×
Newton is defined such that constant = 1.
a MFnet
aMFnet
1.0 kg
10 NScale reading = ?
2.0 kg
10 N
20 N
Scale reading = ?
Free body diagram of 1 kg crate:
WE,C
TS,C (Reading on the scale)
In General The force that the Earth exerts on
an object of mass m is given by
W = m (10 N/kg)
Question: If Jeff jumps off the physics building in
a vacuum, what will his acceleration be? (use Newton’s 2nd law)
10 N/kg is just gWeight force is given by mg
WE,J
Fnet = m aWE,J = m a
m (10 N/kg) = m a
W = m (10 N/kg)= m g
2nd Law is the translator
M = 5 kgT = 100 N
a = 4 m/s/s
Block
WE,B
Trope,B = 100 N
Nfloor,B
ffloor,B
= m g = 50 N
a = 4 m/s/s
How big is the friction force?
= 50 N
Fnet = m a
In the x-direction:
T - f = m a
100 N - f = (5 kg) (4 m/s/s)
f = 80 N
= 80 N
