## Physics laws and formulae (O level)

This list is a list of physics laws and formulae used in O level physics.

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### Kinematics

• $latex average\ speed = \frac{total\ distance\ moved} {time\ taken}$
• $latex velocity = \frac{distance\ moved\ in\ a\ specified\ direction} {time\ taken}$
• $latex velocity = \frac{displacement} {time\ taken}$
• $latex acceleration = \frac{change\ in\ velocity} {time\ taken}$

#### Equations of motion with constant acceleration

• $latex v = u+at$
• $latex s = \frac{(u+v)t}{2}$
• $latex s = ut + \frac{1}{2}at^2$
• $latex v^2= u^2+2as$

### Density

• $latex \rho = \frac{m}{V}$

### Hooke’s law

• Hooke’s law – that the extension was of a material is proportional to the stretching force provided the material is not permanently stretched.
• $latex F = ke$

### Forces

• Parallelogram law – If two forces acting at a point are represented in size and direction by the sides of a parallelogram, their resultant is represented in size and direction by the diagonal of the parallelogram drawn at that point.
• Newton’s first law of motion – A body stays in its state of rest or uniform velocity unless acted upon by an external force.
• Newton’s second law of motion – The acceleration of a body is directly proportional to the resultant force acting on it.
• Newton’s third law of motion – To every action there is an equal and opposite reaction.
• $latex F = ma$
• $latex W = mg$

### Circular motion

• $latex F = \frac{mv^2}{r}$

### Moments

• Law of moments – When a body is in equilibrium the sum of the clockwise moments about any point is equal to the sum of the anticlockwise moments about the same point.
• moment of a force = force × perpendicular distance of the line of action of the force from the pivot

### Momentum

• $latex momentum = mass \times velocity$

### Work, energy and power

• Law of conservation of energy – energy can neither be created nor destroyed but can be converted from one form to another.
• $latex work\ done = force \times distance\ moved\ in\ the\ direction\ of\ the\ force$
• $latex power = \frac{work\ done}{time\ taken}$
• $latex power = \frac{energy\ transfered}{time\ taken}$
• $latex efficiency = \frac{useful\ energy\ output}{total\ energy\ input} \times 100%$
• $latex efficiency = \frac{work\ done\ on\ load}{work\ done\ by\ effort} \times 100%$
• $latex Kinetic\ energy = \frac{1}{2}mv^2$
• $latex Potential\ energy = mgh$

### Pressure

• $latex Pressure = \frac{force}{area}$
• $latex Liquid\ pressure = \rho gh$

### Gas Laws

• Boyle’s law – The pressure of a fixed mass of gas is inversely proportional to its volume if its temperature is kept constant.
• Charles’s law – The volume of a fixed mass of gas is directly proportional to its absolute temperature if the pressure is kept constant.
• Pressure law – The pressure of a fixed mass of gas is directly proportional to its absolute temperature if the volume is kept constant.
• $latex \frac{p_1v_1}{T_1} = \frac{p_2v_2}{T_2}$

### Thermal Physics

• $latex Q = mc \Delta \theta$
• $latex Q = ml$

### Waves and optics

• Law of reflection – The angle of incidence is equal to the angle of reflection.
• $latex v = f\lambda$
• $latex f = \frac{1}{T}$
• $latex refractive\ index = \frac{speed\ of\ light\ in\ vacuum}{speed\ of\ light\ in\ medium}$
• $latex n = \frac{\sin i}{\sin r}$

### Magnetism

• Law of magnetic attraction – Like poles repel, unlike poles attract.

### Electricity

• Law of electrostatic attraction – Like charges repel, unlike charges attract.
• Ohm’s law – The current in an ohmic conductor is directly proportional to the p.d. across its ends if the temperature is kept constant.
• $latex Q = It$
• $latex E = QV$
• $latex E = ItV$
• $latex V = IR$
• $latex R = \frac{\rho l}{A}$
• $latex P = IV$
• $latex P = \frac{V^2}{R}$
• $latex P = I^2R$

#### Resistors in series

• $latex R_{total} = R_1 + R_2 + R_3$

#### Resistors in parallel

• $latex \frac{1}{R_{total}} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3}$

### Electromagnetism

• Faraday’s law – The size of the induced p.d. is directly proportional to the rate at which the conductor cuts magnetic field lines.
• Lenz law – The direction of the induced current is such as to oppose the change causing it.

#### Sydney Chako

Mathematics, Chemistry and Physics teacher at Sytech Learning Academy. From Junior Secondary School to Tertiary Level Engineering Mathematics and Engineering Science.