Forces and Energy Transfer

Chapter 9: Application of Forces and Transfer of Energy

• A force is defined as a push or a pull.
• The SI unit for force is the Newton (N).
• Instruments used to measure force include extension spring balances and compression spring balances.
• Contact forces need physical contact between objects.
• Friction is a force that resists motion between two surfaces in contact.
• Tension force is a pulling force exerted by a string or cable.
• Elastic force occurs within objects that can be stretched or compressed when a force is applied.
• Normal force is a contact force that acts when a surface pushes against an object, acting perpendicularly to the surface of contact.
• Non-contact forces do not require objects to be in contact.
• Gravitational force is an attractive force between two masses, also known as weight.
• Magnetic force is an attractive or repulsive force due to interactions between magnetic fields; like poles repel and unlike poles attract.
• Electric force is an attractive or repulsive force due to interactions between electric fields; like charges repel and unlike charges attract.
• Always label forces in diagrams.

Mass vs Weight

Effect of Forces

• Forces can initiate movement in stationary objects.
• Forces can alter the direction and speed of moving objects, and stop them altogether.
• Forces can deform objects by changing their physical dimensions.
• Forces can apply pressure.
• Pressure is the amount of force acting perpendicularly on a unit area.
• The SI unit for pressure is the Pascal (Pa).
• Pressure = Force / Area.
• When the area decreases, pressure increases, and vice versa, assuming constant force.
• Knives utilize small surface areas, requiring less force to cut.
• Heels exert large pressure due to small surface area on the ground.

Atmostpheric Pressure

• Atmospheric pressure is the force per unit area exerted by the weight of the air above that surface.
• The air exerts pressure on all objects exposed to it which is called atmospheric pressure.
• Atmospheric pressure is higher at sea level than at the top of a mountain.

Pressure in Liquids

• Liquids exert pressure on immersed objects, with pressure increasing at greater depths.
• High pressure can damage submarines.

Energy

• Energy is the measure of the capacity to do work.
• The SI unit for energy is the Joule (J).

Different Forms of Energy

• Heat or internal energy is transferred as heat from a region of higher temperature to a region of lower temperature
• The heat or internal energy is due to the movement of particles; faster particles mean the greater internal energy of the substance
• Chemical potential energy can be converted into other forms of energy through chemical reactions and is present in batteries, food, and fuels.
• Elastic potential energy is stored in stretched or compressed springs and present when an object is stretched or deformed.
• Gravitational potential energy is due to the position of an object above the ground.
• Kinetic energy is energy due to the motion of an object.
• Nuclear energy is present in bonds that hold the nucleus together, and is released when these bonds are broken.

Principle of Conservation of Energy

• Energy cannot be created or destroyed, but can only be converted from one form to another.
• The total energy in an isolated system remains constant.

Example of Energy Conversion

• When a ball rolls down a hill, gravitational potential energy converts to kinetic energy, increasing the speed, and produces heat and sound energy.

Energy Resources and Environmental Impact

Work

• Work is done when an object moves through a distance in the same direction as the force.
• The SI unit of work is the Joule (J).
• Work done = Force × distance moved in the direction of the force
• There is no work done if the distance moved is not in the same direction as the force.
• There is no work done if the force is 0N or the distance moved is 0m
• There is no work done if the force is perpendicular to the distance moved