# Physics FormulasSI Units

This page has all the physics formulas you need. In the first section we have the SI units. In the following section we mechanics equations and electricity equations.

These Physics equations describe the relationship between velocity, acceleration, force, etc. Once we grasp the underlying physics the equations can serve as mental frameworks that we can use to understand and predict the outcome of physical phenomenon. Of course, these equations will also be invaluable when it comes to calculating unknown values from those that are known.

Physics is a science and relies heavily on mathematical skills. The main one being algebra as you need to be able to substitute and rearrange an
equation if necessary. Remember we can always rearrange a formula to suit a particular application.

Note: All these physics formulas require you to use SI units
(International System of Units)

## SI units

 Quantity Quantity symbol Unit symbol Mass m kilograms Kg Force F Newtons N distance d meters m speed v Velocity v Pressure p Pascal Pa Work W Joules J Energy E Joules J Time t Seconds s

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## Mechanics equations

$$v = \frac{\Delta d}{\Delta t}$$

$$velocity = \frac{\text{change in displacement}}{\text{change in time}}$$

$$a = \frac{\Delta v}{\Delta t}$$

$$acceleration = \frac{\text{change in velocity}}{\text{change in time}}$$

$$F = ma$$

$$Force = mass \times acceleration$$

$$W = Fd$$

$$Work = Force \times distance$$

$$P = \frac{W}{t}$$

$$Power = \frac{Work}{time}$$

$$\tau = Fd$$

$$torque= Force \times distance$$

$$F = -kx$$

$$Force = -\text{elasticity constant} \times extension$$

### Circular Motion Equations

 $$a_c = \frac{v^2}{r}$$ $$\text{centripetal acceleration} = \frac{velocity^2}{radius}$$ $$F_c = \frac{mv^2}{r}$$ $$\text{centripetal force} = \frac{mass \times velocity^2}{radius}$$ $$C = 2 \pi r$$ $$Circumference = 2 \pi \times radius$$

### Momentum

$$p =mv$$

$$momentum =mass \times velocity$$

$$\Delta p = F \Delta t$$

$$\text{change in momentum} = Force \times \text{change in time}$$

### Energy Equations

$$E_p = \frac{1}{2}kx^2$$

$$\text{Elastic potential energy} = \frac{1}{2}\text{constant of elasticity}\times extension^2$$

$$E_k = \frac{1}{2}mv^2$$

$$\text{Kinetic Energy}= \frac{1}{2}mass \times velocity^2$$

$$\Delta E_p = mg \Delta h$$

$$\text{gravitational potential energy} = mass \times \text{acceleration of gravity} \times \text{change in height}$$

Ep stands for energy potential which is stored energy. This equation will be able to tell you how much potential energy an object has when it is raised above the ground. Here on earth gravity accelerates all body’s towards the ground at 9.81 m/s^2 if friction is not taken into account.

### Kinematic Equations

$$v_f = v_i + at$$

$$d = v_it+\frac{1}{2}at^2$$

$$d = (\frac{v_i+v_f}{2})t$$

$$v_f^2 = v_i^2 + 2ad$$

$$d = (\frac{v_f+v_f}{2})t$$

## Electricity Equations

$$V = I R$$

$$Voltage = Current \times Resistance$$

$$P = I V$$

$$P =\frac{ \Delta E}{t}$$

$$Power = Current \times Voltage$$

$$Power =\frac{ Energy change}{time}$$

$$R_T= R_1 + R_2 + R_3 + ...$$

Total resistance of resistor in parallel is equal to the sum of the inverse of the resistors resistances.

$$\frac{1}{R_T}= \frac{1}{R_1} + \frac{1}{R_2} +\frac{1}{R_3} + ...$$

Total resistance of resistors in series sum of all resistor in series.

$$E = \frac{V}{d}$$

$$\text{Electric field strength } = \frac{\text{Potential difference (Voltage)}}{distance}$$

$$F = Eq$$

$$\text{Electric force} =\text{Electric field strength} \times charge$$

$$I = \frac{q}{t}$$

$$Current = \frac{charge}{timt}$$

$$V = \frac{\Delta E}{Q}$$

$$V = \frac{energy change}{Charge}$$

$$\Delta E = qEd$$

$$\text{Energy change} = charge \times \text{electric field strength} \times distance$$

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### Rearranging Physics Formulas

Remember: We can rearrange physics formulas by applying simple algebra to ensure that all the symbols on the right hand of the equation are known.
For example, if we know the force acting on an object and the mass of the object how do we work out the acceleration experienced by the object using the equation:

$$F = ma$$

We need to rearrange the equation so that a is on the left hand-side and F is on the right hand-side.

$$a = \frac{m}{F}$$

Now we can plug in the m and F to get a. As long as there is only one unknown we can easily rearrange the equations to give us the answer.

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