# Physical Science Laws and Principles – selected laws

Last updated on August 27th, 2021 at 10:35 am

This post lists down 10 sets of important laws and principles of physical science and briefly explains those.

## Physical Science Laws and Principles

### Newton’s Laws of Motion

**Newton’s first law of motion** states that an object at rest remains at rest and an object in motion remains in motion at a constant speed and in a straight line unless acted on by an unbalanced force.

The first part of the law explains why a football will remain on a tee until it is kicked off or until a gust of wind blows it off.

The second part of the law explains why a bike rider will continue moving forward after the bike comes to an abrupt stop. Gravity and the friction of the sidewalk will eventually stop the rider.

**Newton’s second law of motion** states that the acceleration of an object depends on the mass of the object and the amount of force applied.

The first part of the law explains why the acceleration of a 4 kg bowling ball will be greater than the acceleration of a 6 kg bowling ball if the same force is applied to both balls.

The second part of the law explains why the acceleration of a bowling ball will be larger if a larger force is applied to the bowling ball.

The relationship of acceleration (a) to mass (m) and force (F) can be expressed mathematically by the following equation:*acceleration = force / mass , or a = F / m*

This equation is often rearranged to the form: *force = mass x acceleration, or F = m x a*

Newton’s third law of motion states that whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first.

This law explains that a runner is able to move forward because of the equal and opposite force that the ground exerts on the runner’s foot after each step.

**Law of Conservation of Mass**

Mass cannot be created or destroyed during ordinary chemical or physical changes.

The total mass in a closed system is always the same no matter how many physical changes or chemical reactions occur.

### Law of Universal Gravitation

All objects in the universe attract each other by a force called gravity. The size of the force depends on the masses of the objects and the distance between the objects.

The first part of the law explains why lifting a bowling ball is much harder than lifting a marble. Because the bowling ball has a much larger mass than the marble does, the amount of gravity between Earth and the bowling ball is greater than the amount of gravity between Earth and the marble.

The second part of the law explains why a satellite can remain in orbit around Earth. The satellite is carefully placed at a distance great enough to prevent Earth’s gravity from immediately pulling the satellite down but small enough to prevent the satellite from completely escaping Earth’s gravity and wandering off into space.

### Law of Conservation of Energy

Energy can be neither created nor destroyed.

The total amount of energy in a closed system is always the same. Energy can be changed from one form to another, but all of the different forms of energy in a system always add up to the same total amount of energy no matter how many energy conversions occur.

### Charles’s Law

Charles’s law states that for a fixed amount of gas at constant pressure, the volume of the gas increases as the temperature of the gas increases. Likewise, the volume of the gas decreases as the temperature of the gas decreases.

If a basketball that was inflated indoors is left outside on a cold winter day, the air particles inside the ball will move more slowly. They will hit the sides of the basketball less often and with less force. The ball will get smaller as the volume of the air decreases.

### Boyle’s Law

Boyle’s law states that for a fixed amount of gas at a constant temperature, the volume of a gas increases as the pressure of the gas decreases. Likewise, the volume of a gas decreases as its pressure increases.

If an inflated balloon is pulled down to the bottom of a swimming pool, the pressure of the water on the balloon increases. The pressure of the air particles inside the balloon must increase to match that of the water outside, so the volume of the air inside the balloon decreases.

### Pascal’s Principle

Pascal’s principle states that a change in pressure at any point in an enclosed fluid will be transmitted equally to all parts of that fluid.

When a mechanic uses a hydraulic jack to raise an automobile off the ground, he or she increases the pressure on the fluid in the jack by pushing on the jack handle. The pressure is transmitted equally to all parts of the fluid-filled jacking system.

As fluid presses the jack plate against the frame of the car, the car is lifted off the ground.

### Archimedes’ Principle

Archimedes’ principle states that the buoyant force on an object in a fluid is equal to the weight of the volume of fluid that the object displaces.

A person floating in a swimming pool displaces 20 L of water. The weight of that volume of water is about 200 N. Therefore, the buoyant force on the person is 200 N.

### Bernoulli’s Principle

Bernoulli’s principle states that as the speed of a moving fluid increases, the fluid’s pressure decreases.

The lift on an airplane wing can be explained in part by using Bernoulli’s principle. Because of the shape of the wing, the air moving over the top of the wing is moving faster than the air below the wing. This faster-moving air above the wing exerts less pressure than the slower-moving air below it does. The resulting increased pressure below exerts an upward force and pushes the wing up.

### Law of Reflection

The law of reflection states that the angle of incidence is equal to the angle of reflection. This law explains why light reflects off a surface at the same angle that the light strikes the surface.