Physics Class on Length, Motion, and Forces

Length and time

• A ruler is used to measure lengths between 1mm and 1m
• The volume of an irregular object can be measured by placing it in a measuring cylinder full of water and measuring the rise in water level
• A micrometer screw gauge is used to measure very small distances
• Analogue and digital clocks are used to measure time intervals.
• An average value for a small distance can be found by measuring multiples.

Motion

• Speed is distance traveled per unit time
• Speed is changing means acceleration
• The acceleration of free fall near the Earth is constant
• Distance is measured in mm, cm, m or km and time in ms, s, minutes or hours
• Velocity is speed in a given direction

Forces

• Newton's first law states that an object maintains a constant velocity unless acted on by a resultant force
• Newton's second law states that force equals mass times acceleration
• Newton's third law states that for every action force there is an equal and opposite reaction force
• Friction is a force impeding motion and causing heating
• Air resistance is a form of friction
• The resultant of forces acting on the same line are added when in the same direction and subtracted when in opposite directions
• A force moving an object in a circle with constant speed, results in acceleration towards the center of the circle

Deformation

• Elastic deformation is when an object returns to its original shape after a load is removed
• Plastic deformation is when an object does not return to its original shape after a load is removed
• Hooke's law states that for a spring, force equals spring constant times extension

Scalars and vectors

• A vector has a magnitude and a direction. A scalar has just a magnitude
• Vectors can be represented by arrows
• The resultant of two vectors can be graphically determined by placing them head-to-tail

Momentum

• Momentum is the product of mass and velocity
• Impulse is the product of force and time, equal to the change in momentum
• In a collision, total momentum before equals the total momentum after (law of conservation of momentum)
• In elastic collisions, total kinetic energy before equals the total kinetic energy after

Energy, work and power

• Energy can be transferred between different forms including kinetic, gravitational potential, chemical, elastic potential, nuclear and internal energy as a result of an event or process
• Work done equals force times distance
• Power is the rate at which energy is transferred or the rate at which work is done
• Energy is always conserved. The total energy before is equal to the total energy after
• The efficiency of a system is the ratio of useful work done to the total energy supplied.

Energy sources

• All energy on Earth is originally from the Sun, with the exception of geothermal, nuclear and tidal energy
• Renewable energy sources are replenished as quickly as they are used.
• Non-renewable energy are used more for large-scale energy supplies.
• Non-renewable energy sources are becoming less popular due to scarcity and environmental harm.
• The original source of energy released in fossil fuels is the Sun.
• Energy from nuclear power stations is released through nuclear fission, while energy from the Sun is released through nuclear fusion.

Pressure

• Pressure in fluids causes a net force at right angles to any surface
• Pressure equals force divided by area
• Atmospheric pressure is measured using a barometer
• The pressure beneath a liquid surface increases with depth and density.