forces and pressures

• A force is a push or a pull acting on an object
• The SI unit for force is Newton (N)
• Force is measured by a spring balance or dynamometer
• Contact force is a force that results when two interacting objects are in direct contact with each other. Examples are elastic force, frictional force
• Non-contact force is a force applied to an object by another object that is not in direct contact with it. Examples are magnetic force, gravitational force
• Friction is a force that opposes motion between two surfaces in contact.
• Advantages of friction

  It allows us to hold onto objects like cups and books or aiding in daily activities such as enabling pencils to make marks on paper
• Disadvantages of friction are wear and tear on objects like shoes and tires, wastage of energy as more energy is needed to move objects due to friction, and the production of heat resulting in energy wastage
• Ways to overcome friction include using lubricating oil or grease, employing ball bearings, rollers or wheels, and using a cushion of air
• Elastic force is the force acting on a stretched or compressed elastic object to return to its original shape
• An example of the use of elastic force

  Rock climbers use climbing ropes that can stretch and exert elastic force. When a climber falls, the rope stretches and the elastic force exerted increases. This reduces the impact felt by the climber when he falls
• Gravitational force is a force that attracts two objects towards each other. The magnitude of the gravitational force is affected by the mass of an object and the distance between two mases
• Gravitational field strength is the amount of gravitational force acting on a 1kg mass
• Density (kg/m^3) = mass(kg) / volume(m^3)
• Magnetic force is the force of attraction between magnets and magnetic substances such as iron or steel. Unlike poles attract each other, while like poles repel each other
• Effects of force:

  • Move a stationary object
  • Change the direction of the object
  • Change the speed of an object
  • Change the size of an object
  • Change the shape of an object
  • Stop a moving object
• Turning effects of forces:

  • A moment is the ability of a force to make an object turn
  • The SI unit of moment is newton-metres (Nm)
  • A pivot is a fixed point allowing an object to turn
  • The moment of a force depends on perpendicular distance from the pivot to the line of the applied force and the magnitude of force applied
  • Formula: moment of force = force x distance
  • Two types of moments: clockwise and anti-clockwise
  • The further the force is from the pivot, the larger the moment of the force is, making it easier to turn an object
  • Turning effect can help carry out actions with little force like removing a lid or tightening a nut
• Pressure:

  • Pressure is an effect of force acting on an object
  • The SI unit of pressure is pascal (Pa)
  • Formula of pressure: force/area
• Work:

  • Work is a transfer of energy from one object to another or from one form to another
  • The SI unit of work is Joule (J)
  • Conditions for work to be done on an object: force applied, object moves in the same direction as the force applied