Equations You Must Memorise

The Edexcel GCSE Physics (1PH0) exam provides an equation sheet, but it does NOT contain all the equations you need. The equations listed in this lesson must be committed to memory — they will not be given to you in the exam. For each equation, you need to know what the symbols represent, the correct units, and how to use it in a calculation.

---

Forces and Motion

Weight

W = mg

Symbol	Quantity	Unit
W	Weight	Newtons (N)
m	Mass	Kilograms (kg)
g	Gravitational field strength	N/kg (9.8 N/kg on Earth)

Worked example: Calculate the weight of a 55 kg person on Earth.

W = mg = 55 × 9.8 = 539 N

Exam Tip: Weight and mass are NOT the same thing. Mass is the amount of matter (in kg) and is constant everywhere. Weight is a force (in N) and depends on the gravitational field strength.

---

Work Done

W = Fs

Symbol	Quantity	Unit
W	Work done	Joules (J)
F	Force	Newtons (N)
s	Distance (in the direction of the force)	Metres (m)

Worked example: A person pushes a box with a force of 40 N over a distance of 3 m. Calculate the work done.

W = Fs = 40 × 3 = 120 J

---

Speed

v = s / t

Symbol	Quantity	Unit
v	Speed (or velocity)	Metres per second (m/s)
s	Distance	Metres (m)
t	Time	Seconds (s)

Worked example: A cyclist travels 200 m in 25 s. Calculate the speed.

v = s / t = 200 / 25 = 8 m/s

---

Acceleration

a = Δv / Δt (or a = (v − u) / t)

Symbol	Quantity	Unit
a	Acceleration	m/s²
Δv	Change in velocity	m/s
Δt	Time taken	s
v	Final velocity	m/s
u	Initial velocity	m/s

Worked example: A car accelerates from 10 m/s to 30 m/s in 8 s. Calculate the acceleration.

a = (v − u) / t = (30 − 10) / 8 = 20 / 8 = 2.5 m/s²

---

Energy

Kinetic Energy

KE = ½mv²

Symbol	Quantity	Unit
KE	Kinetic energy	Joules (J)
m	Mass	Kilograms (kg)
v	Speed	m/s

Worked example: Calculate the kinetic energy of a 1200 kg car travelling at 15 m/s.

KE = ½mv² = ½ × 1200 × 15² = ½ × 1200 × 225 = 135,000 J (135 kJ)

Exam Tip: Remember to square the velocity BEFORE multiplying by the mass. A very common mistake is to multiply mass by velocity first and then square the result.

---

Gravitational Potential Energy

GPE = mgh

Symbol	Quantity	Unit
GPE	Gravitational potential energy	Joules (J)
m	Mass	Kilograms (kg)
g	Gravitational field strength	N/kg
h	Height	Metres (m)

Worked example: A 2 kg book is lifted onto a shelf 1.5 m high. Calculate the GPE gained. (g = 9.8 N/kg)

GPE = mgh = 2 × 9.8 × 1.5 = 29.4 J

---

Power (two forms)

P = E / t and P = W / t

Symbol	Quantity	Unit
P	Power	Watts (W)
E	Energy transferred	Joules (J)
W	Work done	Joules (J)
t	Time	Seconds (s)

Worked example: A motor transfers 5000 J of energy in 20 s. Calculate the power.

P = E / t = 5000 / 20 = 250 W

Exam Tip: Power is the RATE of energy transfer. A 100 W light bulb transfers 100 joules of energy every second.

---

Waves

Wave Speed

v = fλ

Symbol	Quantity	Unit
v	Wave speed	m/s
f	Frequency	Hertz (Hz)
λ	Wavelength	Metres (m)

Worked example: A wave has a frequency of 500 Hz and a wavelength of 0.66 m. Calculate the wave speed.

v = fλ = 500 × 0.66 = 330 m/s

---

Density

Density

ρ = m / V

Symbol	Quantity	Unit
ρ (rho)	Density	kg/m³ (or g/cm³)
m	Mass	kg (or g)
V	Volume	m³ (or cm³)

Worked example: A metal block has a mass of 500 g and a volume of 64 cm³. Calculate the density.

ρ = m / V = 500 / 64 = 7.8 g/cm³

---

Pressure

Pressure

P = F / A

Symbol	Quantity	Unit
P	Pressure	Pascals (Pa)
F	Force	Newtons (N)
A	Area	m²

Worked example: A box exerts a force of 200 N on the floor. The area of the base is 0.4 m². Calculate the pressure.

P = F / A = 200 / 0.4 = 500 Pa

---

Electricity

Charge

Q = It

Symbol	Quantity	Unit
Q	Charge	Coulombs (C)
I	Current	Amps (A)
t	Time	Seconds (s)

Worked example: A current of 3 A flows for 120 s. Calculate the charge.

Q = It = 3 × 120 = 360 C

---

Potential Difference (Ohm's Law)

V = IR

Symbol	Quantity	Unit
V	Potential difference	Volts (V)
I	Current	Amps (A)
R	Resistance	Ohms (Ω)

Worked example: A 6 V battery drives a current of 0.5 A through a resistor. Calculate the resistance.

R = V / I = 6 / 0.5 = 12 Ω

---

Electrical Power (two forms)

P = IV and P = I²R

Symbol	Quantity	Unit
P	Power	Watts (W)
I	Current	Amps (A)
V	Potential difference	Volts (V)
R	Resistance	Ohms (Ω)