Applications of forces and transfer of energy

• Elastic potential energy can be transferred from one object to another through contact forces such as pushing or pulling.
• The unit of work is the joule (J).
• Work is the amount of energy transferred or the amount of force acting through a distance.
• Gravitational potential energy (GPE) is the amount of energy that an object has due to its position relative to Earth's surface.
• When an object falls, GPE decreases while kinetic energy increases.
• The surface of earth consists of many large pieces of rocks known as technonic plates.
• These plates float on a semi liquid layer known as the asthenosphere.
• The technonic plates move very slowly and continuously.
• Global warming results in an increase in surface temperature of the seas/oceans. This leads to longer and more intense storms that begin over warmer oceans in tropical regions.
• Tropical cyclones are accompanied by heavy rain and strong winds.
• In a tropical cyclone, wind speeds can go up to about 200 km/h and damages vehicles and buildings in their path.
• A force is a push or pull.
• All forces can be measured by spring balances/newton meter.
• The SI unit for force is newton (N).
• Forces can be classified as a contact force or a non-contact force.
• Friction: it is classified as a contact force. It is the force that opposes motion between two surfaces in contact. At microscopic level, there are many bumps along the surface. These bumps causes the two surfaces to be stuck at various points along the motion. This produces friction.
• Ways to reduce friction: using ball bearings, lubricants or streamlined shapes to reduce water/air resistance.
• Elastic force/tension: when an elastic object is stretched or compressed, it resists the change in shape by exerting a force in the opposie direction. This force is known as elastic force or tension in the object. Elastic force is the force acting on a stretchedd or compressed elastic object to return to its original state/shape. Elastic force is a contact force. It can be found in stretched bow, compressed/stretched springs.
• The force that pulls all objects towards the earth is called gravitational force. Force of gravity exists between any two objects with mass. Gravitational force is a non-contact force. Weighr of an object is the gravitational force acting on the object. Since weight is an object is the gravitational force acting on the object. Since weight is a force, it is measured using a spring balance. The unit of weight is the newton (N). The greater the mass of an object, the greater its weight on earth.
• Electrical force is a non-contact force. 2 charged objects can experience electrical force of repulsion or attraction without direct contact between them. Like charges repel, unlike charges attract.
• Magnetic force is a non-contact force. 2 magnets can experience magnetic force of repulsion or attraction without direct contact between them. Like poles repel, unlike poles attract.
• Magnetic force: a magnet can attract objects made from iron, steel, cobalt and nickel. These materials are known as magnetic materials. Magnets can only interact with magnetic materials or other magnets.
• 'Maglev' comes from the words 'magnetic levitation' (rising and floating). Magnets in the track and train repel and lift the train slightly above the track. As there is no contact between the track and vehicle, contact friction is greatly reduced. This allows the train to move very fast (up to 500 km/h). Maglev trains experience mainly air resistance rather contact friction with the track.
• Mass is a measure of amount of matter in an object. Mass is measured by a beam balance or electronic balance. Conceptually, think of amount of matter in an object = number of atoms/molecules that made up the object. The SI unit for mass is kg. Mass of an object is always a constant regardless of location. An object in outer space far away from any planets or stars experiences no gravitational force! Thusx it is possible for an object to have mass but no weight.
• When 2 or more masses interacts, they exert a mutually attractive force on each other. These forces are known as gravitationalnforces or weight. The relationship between mass and weight is directly related/proportional: weight x mass. Thus, the equation is w = m x g. On earth, the constant calue of gravitt is 10 N/kg.
• When an object is in motion, it means the object is moving. When an object undergoes changes in motion, it means the object changes the way it moves. Motion on an object is characterized by how fast an object is moving and the direction of its movement. Examples of changes in motion:

  -an object initially at rest starts to move

  -an object moving at constant speed starts to slows down

  -an object moving at constant speed starts to speed up

  -a moving object changes its direction of movement
• When there are no changes to motion, an object can only

  •remain stationary if it is initially at rest

  •move with constant speed in a straight line if it is initially moving.
• Motion of an object consist of its speed and its direction of travel. A net force is needed to cause a change in motion. Thusx without a net force, the motion of an ibject remains unchanged. Without a net force acting on an object, if the object is moving, it can only move with constant speed in a straight line. When there are changes to motion of an object, there is a net force acting on the object. When there is a net force acting on an object, there will be changes to the motion of the object.
• Pressure: pressure is an effect of force acting on an object.
• Pressure: the amount of force acting per unit area is known as pressure. A pin can be easily pushed into a board while a piece of block cannot, dven if a large force is used. The point of the pin has a small area so the force acts on a small area. The eraser has a larger area so the force exerts a smaller pressure.
• Calculation of pressure: pressure depends on force and area. Its SI unit is Pascal(Pa) or newton per square meter. The formula is pressure= force divide contact area.

  •P is pressure in Pascal (Pa)

  •F is force in Newton (N)

  •A is contact area in square metre (m2).
• Pressure in liquid: when swimming nearer the bottom of the pool, you experienced a higher water pressure with an increasing depth of water.
• Atmospheric pressure: earth is surrounded by a thick layer of air. Air particles are light but they stil occupy space and have mass. Thus, the layer of air particles pushes down on earths surface due to gravitationalnforce. The force exerted by the layer of air per unit area is the atmospheric pressure.
• Energy and force are not the same thing. But they related theough a process known as work done. Through the application of force on an object, work is done on the object to transfer energy to the object.
• Work done should be regarded as a process of energy transfer. Work is the use of a force to move an object in the direction of the force. The conditions for work to be done are as follows:

  •there is a force acting on an object

  •the object moves through a distance

  •the object moves in the direction of the force

  The three conditions are needed for work to be done. If any of these conditions are missing, no work is done.
• Law of conservation of energy states that energy cannot be created or destroyed, energy can be converted from one form to another or tranferred from one object to another.