Grade ten Physics

Concepts of forces

Force and its effects | Grade 10 Physics

A force is a push, a pull or a twist exerted on a body. The SI unit for force is newton (N), which is the force required to accelerate a one-kilogramme mass at a rate of one metre per second.
Hooke’s Law states that: the amount of deformation of an elastic object is proportional to the forces applied to deform it. i.e.
Newton’s First Law of Motion states that: “if no net force acts on an object, it maintains its state of rest or its constant speed in a straight line”.
Inertia is a property that causes a body to resist changes in its state of motion and it depends directly with the mass of the object.
Newton’s Second Law of Motion states that: “the acceleration of a body resulting from an applied force is proportional to that force, and inversely proportional to the mass of the body” F=ma
Newton’s Third Law of Motion states that: “for every action force there exists a reaction force that is equal in magnitude but opposite in direction to that force”.
Friction is a force which acts parallel to surfaces that are in contact and a direction opposite to the motion of the object or to the net force tending to produce the motion.
The ratio of the frictional force to the normal contact force is called the coefficient of friction(μ); μ=F_f/F_N
An object travelling along a circular path at a constant speed has an acceleration directed towards the centre of the circular path called centripetal acceleration: a=v^2/r . This acceleration results from a force directed towards the centre of the circular path called centripetal force : F=〖mv〗^2/r
The centrifugal force is the apparent force that draws a rotating body away from the centre of rotation. It is caused by the inertia of the body as the body’s path is continually redirected and it is equal in magnitude but opposite in direction to the centripetal force.
When a car travels around a bend in the road, the maximum safe speed for the car is given by: v=√μgr
The angular velocity (ω) is the angle turned through per unit time. It is measured in radian per second. ω=v/r. One revolution =2π radians(rad).

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Pressure

Pressure in Fluids – Physics 10

A fluid is a substance that offers no permanent resistance to deforming force. Fluids include liquids and gases.
Pressure is defined as force or thrust acting per unit area, the force being at right angles to the area i.e. Pressure=Force/Area. The SI unit for pressure is pascal (Pa) which equals one newton per square metre.
A pressure exerted on us and over the surface of the earth by air molecules in the atmosphere is known as the atmospheric pressure. The atmospheric pressure decreases with the increase in altitude and its unit is the atmosphere (atm) equivalent to 760mmHg or 101325Pa.
Pascal’s principle: “Pressure exerted on a contained fluid is transmitted undiminished throughout the fluid, acting in all directions and perpendicular to the walls of the container”. This has applications in hydraulic machines and jacks, syringe, drinking straws, etc.
Gauge pressure is the pressure relative to atmospheric pressure.
Absolute pressure is the sum of gauge pressure and atmospheric pressure.
Open-tube manometers have U-shaped tubes and one end is always open. It is used to measure pressure.
A mercury barometer is a device that measures atmospheric pressure.
Archimedes’ principle: “When a body is wholly or partly submerged in a fluid the upthrust equals the weight of fluid displaced (i.e. pushed aside)”. This principle is applied in ships designing, hot air balloon, submarine, etc.
Principle of floatation: “A floating body displaces its own weight of fluid.” A material floats in a fluid if its density is the same as or less than that of the fluid.
The pressure of fluids increases with depth, i.e. P=hgρ

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Work Energy and Power

Work and Energy and Power | Physics 10

Work is the action of force moving an object. It is a measure of energy transfer. Work=force×distance. The SI unit for work is the joule, equivalent to Nm.
Work can also be measured in kilowatt hour since joule is very small quantity of work. One kilowatt hour is the amount of work done by a machine with a power of 1kW in 1h. 1kW∙h=3600000J=3.6MJ
Energy is the ability to do work and is measured in joules.
The energy due to position or elevation is called gravitational potential energy (PE orE_g ) and is calculated from: E_g=mgh.
Kinetic energy (KE or Ek) is the energy of a moving object. The kinetic energy of an object depends on its mass and its speed or velocity, i.e. E_k=1/2 〖mv〗^2
Total mechanical energy (ET or TME) is the sum of the kinetic and potential energy and it is constant at all points of a falling or moving body. E_T=E_g+E_k
The law of conservation of energy states that: “In any transfer or transformation of energy, the total amount of energy remains constant”.
In a nuclear reaction, so much energy is released, hence violating the law of conservation of energy. This is explained in the theory of relativity established by Albert Einstein in 1905, stating that: “a decrease in mass of a system might show up as an increase in the energy of the system”. So mass is another form of energy. That energy is calculated from : E=mc^2
Power is the rate at which the work is done i.e. Power=(work done)/(time taken). The SI unit of power is the watt, equivalent to the joule per second.

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Length and time

LENGTH AND TIME, THEIR USE IN PHYSICS

There is an international system of units called the SI units (système International d’unités) which is most commonly used around the world and by scientists since 1968.
Measurable features or properties of objects are often called physical quantities. All physical quantities should be quoted with their numerical value and their unit.
Base quantities or fundamental quantities are those which are used to define all other quantities (or derived quantities)
When dealing with very large or small number, express them in powers of ten known as “scientific notation or standard form”: M×〖10〗^n, where M is a number having a single non-zero digit to the left of the decimal point and n is a positive or negative exponent.
Significant figures are those digits in a number that are known with certainty plus the first digit that is uncertain.
Length is defined as a linear measurement of the distance between two points. Its SI unit is called the metre. Instruments used to measure length include the ruler, the engineer’s callipers, the micrometer screw gauge and the vernier callipers.
Time is the measure of how long an event lasts and is measured in seconds. The measuring instruments of time include clocks and the pendulum.
The time taken for the pendulum to oscillate once is the period (T) and is calculated from T=(Total time)/(number of oscillations) or t/n or T=2π√(l/g) and the number of oscillations made in one second is called its frequency and is measured in Hz; f=1/T or n/t

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Scientific Measurements

SCIENTIFIC MEASUREMENTS

• The système International d’Unités’ (International System of units) shortened to S.I. units is the metric system recommended at The conférence Générale des Poids et des Mesures (CGPM)’ (General Conference on Weight and Measures) as standard for use in any scientific measurements.
• The SI Units uses seven base units from which all other units are derived from by multiplying or dividing one unit by another without introducing a numerical factor.
• The SI base units are: Length, Mass, Time, Electric current, Thermodynamic temperature, Luminous intensity and Amount of substance
• A system of prefixes has been created to simplify the expression of the physical values written in standard form.
• The physical values written in the scientific notation or standard form are expressed in powers of ten in a way to assess the order of magnitude and to visually decrease the zeros that are got in the answer to some problems.
• Accuracy is how close the value is to the actual value (remember A and a).
• Precision is how close values are in an experiment to each other. Precision is dependent on the significant digits of the instrument or measurement.
• If a number is very large or has infinite number of digits, then this number is made simpler by only referring to a specified number of digits.

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Introduction to Physics

INTRODUCTION TO PHYSICS – GRADE TEN PHYSICS

Physics is defined as a natural science that involves the study of nature and its motion through space-time, along with related concepts such as energy and force.
Physics principles are applied in our everyday activities such as cooking, driving, etc.
The main activity of a physicist is based on experiment in order to understand the theoretical explanations and it is mainly conducted in the laboratory.
The main causes of accidents in the laboratory are carelessness and ignorance and the most common sources of errors are Systematic, human and random errors.
When conducting an experiment remember to put on protective clothing such as overcoat, apron and gloves; and protect your eyes using goggles.
The results of experiments can be recorded using a table and used to plot a graph. From graph you can calculate the slope or gradient using the formula: Gradient G=y_(2-y_1 )/x_(2-x_1 ) =Y/X
Interpolation: is the process of using the graph to predict the reading of measurements that lie between those actually made.
Extrapolation: is the extension of the graph to include the range of the data required (common when obtaining zero on Kelvin scale)
The right-angled triangle is used to define the trigonometric functions which are common mathematical tools used in physics: sinθ=(opposite leg)/hypotenuse cosθ=(Adjascent leg)/hypotenuse tanθ=(Opposite leg)/(Adjascent leg)
Area is the extent or measurement of a flat surface bounded by length and breadth and its SI unit is the square metre.

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