forces in one dimension - physicsatthebay.com in 1 -d.pdf · net=8−5=3n if the forces are at an...
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Forces in one Dimension
Chapter 4
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Force: push or pull. It is a vector.
Contact Force: when object touches system(friction, tension, spring,normal...)
Field Force: exerted without contact( gravitational, magnetic, electric)
Net Force: Vector sum of all forces on object.
Net
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First: An object at rest will remain at rest, and an object that is moving will continue to move in a straight line at the same speed, if the net force acting on the object is zero.(Inertia).
Second:
Third:
Newton’s Laws
F = maFA on B = −FB on A
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FT = Force of TensionFF = Force of FrictionFN = Normal(90 deg rees) contact ForceFg = Force of Gravity
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Net Force
5N 8N
Fnet = 8 − 5 = 3N
If the forces are at an angle to each other you need to split the forces into x and y components. It’s your choice about
the x and y directions.
If we have a slope x is along slope.y is perpendicular to slope.
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Using Newton’s Second Law
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If you know the mass, you also know the weight
Weight = mass x acceleration
If you know the weight, you also know the mass
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Fnet = ma
net force
Newton’s Second Law
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Gravity
• Earth’s gravity acts downward toward the center of the Earth.
• Gravity causes objects to accelerate downwards, whereas air resistance acts in the opposite direction to motion.
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If two forces are perpendicular you have to use Pythagoras to find the net force.
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Say the mass of the bucket is 10kg
Weight = Fg = mgFg = 10(9.8) = 98N 98N
Say the acceleration is +2m/s2 upward
This tells us the net force Fnet = maFnet = 10(2) = 20N
20N
We now know the tension in the rope
118N
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M = 50kg M = 70kg
a = 4m / s2 towards the boy
N’s third law says that action &reaction are equal and opposite
So, the force toward the boy equals the force toward the girl
Fboy = maFboy = 70(4) = 280N
Fgirl = ma280 = 50(a)5.6m / s2 = a
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FrictionFN = normal force
Fg = mi9.81
FFfriction
Static Kinetic
Fs = µs iFN
Fk = µk iFNThis gets bigger and bigger until it reaches a maximum and the object
moves.
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Fg
FNThis is your basic
slope diagram.If the object is
moving down the slope you will need to put in
friction going up the slope
Adj. =Fg Cos
Opp.=Fg Sin