3.2 Forces in action

Cards (44)

  • force (N)= mass (kg) x acceleration (ms2ms^{-2})
  • A force of 1N will give a 1kg mass an acceleration of 1ms2ms^{-2} in the direction of the force
  • weight is a force based on the gravitational pull of the planet
  • mass the the amount of matter an object is made of
  • Weight (N) = mass(kg) x gravitational field strength (N/kg)
  • A newtonmeter shows the gravitational force acting on an object, in Newtons
  • Weight is the gravitational force acting on an object through its centre of mass
  • Friction is the force that arises when two surfaces rub against each other
  • Drag is a resistive force on an object travelling through a fluid
  • Tension is the force within a stretched cable or rope
  • Upthrust is the upward buoyancy of an object in a fluid
  • normal contact force is the force that arises when objects rest against each other
  • A fluid is a liquid or gas
  • magnitude of drag depends on speed, cross sectional area, texture, and density of the fluid
  • drag = speed2^2
  • Terminal velocity is reached when air resistance equals weight in the opposite direction
  • The centre of gravity is the point where the entire weight of an object appears to act
  • The centre of mass is the point at which any externally applied force produces a straight line motion but no rotation
  • experiment to find the centre of gravity : pins in an object and use a plumbline to draw lines - centre is the point of intersection
  • Conditions for equilibrium
    • resultant force of zero - horizontally and vertically
    • no rotation
  • When an object is in equilibrium, the forces acting on it form a closed triangle
  • The moment of a force is the turning effect of a force about some axis or point
  • The SI unit for a moment of a force is Nm
  • moment = force x perpendicular distance to the line of action of the force
  • The Principle of Moments
    For a body in rotational equilibrium, the sum of the anti clockwise moments about any point its equal to the sum of the clockwise moments about that same points
  • Principle of Moments
    ΣMclockwise=\Sigma M_{clockwise}=ΣManticlockwise\Sigma M_{anticlockwise}
  • Applying a pair of equal but opposite forces parallel to each other along different lines causes a rotation without any translational motion
  • A couple is pair of equal but opposite forces parallel to each other that act along different lines
  • Torque of a couple = one of the forces x the perpendicular separation between the forces
  • Density = mass / volume
  • To find the volume of an irregular object, put the object in a container with a known volume of liquid and calculate the increase of volume
  • Pressure is the normal force exerted per unit of cross sectional area
  • Pressure
    ρ=\rho =F/AF/A
  • Gases and liquids exert pressure on surfaces as there is a constant movement of particles which collide with the surface
  • Pressure exerted by a vertical column of liquid = height of the column x density of the liquid x the value of acceleration under free fall
  • Pressure doesn't depend on the cross sectional area
  • density is directly proportional to height of a vertical column of liquid so pressure increases with depth
  • Denser liquids will exert greater pressure
  • Upthrust is the resultant force due to pressure of an object submerged in a fluid
  • Objects submerged in fluids exert pressure on the fluid which exerts pressure on the object which causes an upward force