A level Physics Forces

• Net force

  The sum of all the forces acting on an object
• The net force is equal to F = ma
• Newton

  The force required to accelerate a mass of one kilogram by one meter per second squared
• Types of forces

  • Weight
  • Normal force
  • Upthrust
  • Tension
  • Friction
• Free body diagram

  • Shows the forces acting on an object, with the forces in the correct proportion
• Constant velocity

  No resultant force, so no acceleration
• Drag force

  Force that opposes the motion of an object through a fluid
• Investigating the motion of an object falling through a fluid

  1. Fill a tube with viscous fluid

  2. Drop a ball bearing and record time to reach intervals

  3. Plot speed vs time graph to find terminal velocity
• Analyzing forces on an object on an inclined plane

  1. Split the weight into components parallel and perpendicular to the plane

  2. Parallel component = mg sin(theta)

  3. Perpendicular component = mg cos(theta)
• Splitting weight into parallel and perpendicular components

  1. Find angle theta

  2. Parallel component = mg sin theta

  3. Perpendicular component = mg cos theta
• Center of gravity

  Point at which the entire weight of an object seems to act
• Determining center of gravity

  1. Pin object

  2. Hang plumb line vertically downwards

  3. Rotate object and pin at different point

  4. Intersection of lines is center of gravity
• Moment of force

  Product of the force and perpendicular distance from the pivot point to the line of action of the force
• Clockwise moment

  Force applied in clockwise direction
• Anti-clockwise moment

  Force applied in anti-clockwise direction
• Moment = Force x Perpendicular distance
• For equilibrium, sum of anti-clockwise moments = sum of clockwise moments
• Force couple

  Two equal and opposite forces acting in the same plane
• Torque

  Net moment, equal to magnitude of one force x distance between forces
• Density

  Mass per unit volume, in kg/m^3
• Pressure

  Force per unit area, in N/m^2 or Pascals
• Archimedes' principle

  Upthrust on submerged object = weight of displaced fluid