1.2.3 Equilibrium. Objective Draw and use a triangle of forces to represent the equilibrium of three...
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Transcript of 1.2.3 Equilibrium. Objective Draw and use a triangle of forces to represent the equilibrium of three...
Objective
Draw and use a triangle of forces to represent the equilibrium of three forces acting at a point on an object
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Make a list of all the different types of forces you can think of:
Pushes and pulls Weight Friction Drag Upthrust Contact/Reaction Force Tension
Write a sentence or two about each force, with examples
Turning Forces
Explain that a couple is a pair of forces that tends to produce rotation onlyDefine and apply the torque of a coupleDefine and apply the moment of force
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A couple occurs when two forces are equal and opposite to each other, but are not in the same straight line
Upward force balances downward force Resultant equals zero Tend to produce rotation
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A couple is a pair of equal and parallel but opposite forces, which tend to produce rotation only
x
x
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Describes the turning effect of a couple Measured in Newton metres Used to describe turning forces e.g. car engines
torque = one of the forces x perpendicular distance between the forces
6 N
6 N
2 m torque = force x perp. distance= 6 N x 2 m= 12 Nm
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The moment of a force is the turning effect of a single force
Measured in Newton metres Principle of Moments states that:
For a body in rotational equilibrium, the sum of the clockwise moments equals the sum of the anticlockwise moments
F
x
p
F
p x
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The moment of a force is the force multiplied by the perpendicular distance from a stated point
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A wheelbarrow is loaded as shown
a) Calculate the force that the gardener needs to exert to hold the legs off the floor
b) What force is exerted by the ground on the legs of the barrow (taken both together) when the gardener is not holding the handles?
400N
1.20m
0.50m
0.20m
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Physics 1 SAQ 5.5 & 5.6 Page 56 questions 1 to 4
OCR AS Physics Page 41 questions 4 - 7
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Density = mass
volume
where density (ρ) is in kg m-3
mass (m) kg
volume (V) m3
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Density of solids and liquids varies little with temperature
Density of gases varies considerably
Pressure
Select and use the equation for pressure – p = F/A
where F is the force normal to the area A
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Pressure = force
area normal to force
where pressure (p) is in Pa or N m-2
force (F) N
area (A) m2
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sics Pressure at a depth in a fluid
volume = Ah
mass m = Ahρ
weight = mg = Ahρg = force F
pressure on base of column
= Ahρg / A
= hρg
A
Liquid of density ρ
h
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For equilibrium, force upward = weight downward
So, calculate force upward from weight downward