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1.2.3 Equilibrium

1.2.3 Equilibrium. Objective. Draw and use a triangle of forces to represent the equilibrium of three forces acting at a point on an object. Forces. Make a list of all the different types of forces you can think of: Pushes and pulls Weight Friction Drag Upthrust Contact/Reaction Force

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1.2.3 Equilibrium

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  1. 1.2.3 Equilibrium

  2. Objective Draw and use a triangle of forces to represent the equilibrium of three forces acting at a point on an object

  3. Forces 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

  4. Triangle of Forces • Consider the Worked Example on page 61 of “Physics 1”

  5. Turning Forces Explain that a couple is a pair of forces that tends to produce rotation only Define and apply the torque of a couple Define and apply the moment of force

  6. Couple • 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

  7. Couple - definition • A couple is a pair of equal and parallel but opposite forces, which tend to produce rotation only x x

  8. Torque • 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 torque = force x perp. distance = 6 N x 2 m = 12 Nm 2 m 6 N

  9. Moment of a Force • 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 x F p x p F

  10. Moment of a Force - definition • The moment of a force is the force multiplied by the perpendicular distance from a stated point

  11. Example A wheelbarrow is loaded as shown • Calculate the force that the gardener needs to exert to hold the legs off the floor • What force is exerted by the ground on the legs of the barrow (taken both together) when the gardener is not holding the handles? 0.20m 400N 0.50m 1.20m

  12. Questions • Physics 1 • SAQ 5.4 to 5.8 • Page 70 question 4

  13. Density Select and use the equation for density ρ = m/V

  14. Density Density = mass volume where density (ρ) is in kg m-3 mass (m) kg volume (V) m3 rho

  15. Density • Density of solids and liquids varies little with temperature • Density of gases varies considerably

  16. Pressure Select and use the equation for pressure – p = F/A where F is the force normal to the area A

  17. Pressure Pressure = force area normal to force where pressure (p) is in Pa or N m-2 force (F) N area (A) m2

  18. 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 h Liquid of density ρ

  19. Floating For equilibrium, force upward = weight downward So, • calculate force upward from weight downward

  20. Questions AS Physics 1 • Page 69 • Questions 1, 2 & 3 Assessment • Chapter 5 worksheet • EoC Test – Chapter 5

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