# IGCSE Edexcel Combined Double

### Wave Speed

Wave speed is given in meters per second (the number of waves that pass per second). Wavelength is measured in meters and frequency is measured in hertz (Hz), or number of waves per second.

### Turning Moments

The size of the turning effect is called a turning moment. As Newton’s first law of motion states, an object will remain at rest if the forces are balanced. When the sum of the forces add to zero, a body will remain at rest or move at a constant velocity.

### Pressure

Pressure can be calculated if you know the force applied to or by an object and the contact area. The units are newtons per square meter, or N/m2.

### Force, Mass and Acceleration

An object of constant mass accelerates in proportion to the force applied.

### Kinetic Energy

In physics, the kinetic energy (KE) of an object is the energy that it has due to its motion. It is defined as the work needed for an object of a known mass to accelerate to a given velocity.

### Power

The quantity power is the rate at which work is done. The quicker work is done the greater the power.

### Charge

The size of the current is the rate of flow of charge. Electrons are negatively charged particles which transfer energy through wires as electricity.

### Resistance

Resistance is an electrical quantity that measures how a device or material reduces the electrical current flow through it.

### Electrical Power

The power of an appliance is the energy that is transferred per second. Electric power is the rate, per unit time at which electrical energy is transferred by an electric circuit.

### Density

Density is a measure of how compact the particles are in a substance. Density is defined as the mass per unit volume.

### Half Life

The radioactivity of a sample decreases over time. Half life is a measurement of this decrease.

### Gravitational Potential Energy

Lifting an object in a gravitational field transfers energy into the objects gravitational energy store. Gravitational potential energy is the energy an object has due to its height above Earth.

### Efficiency

The efficiency of a device is the proportion of input energy that is converted to useful energy.

### Energy Transformed

The potential difference between two points is the energy transferred per unit charge. An electrical circuit is an energy transformation device.

### Forces and Work Done

The unit for work done is the joule (J), or Newton meter (N-m). One joule is equal to the amount of work that is done when 1 N of force moves an object over a distance of 1 m.

### Wave Period

The period of a wave is the time it takes to complete one cycle. The unit for a wave period is seconds, and it is inversely proportional to the frequency of a wave, which is the number of cycles of a wave that occur in one second.

### Uniform Acceleration

Uniform or constant acceleration is a type of motion in which the velocity of an object changes by an equal amount in every equal time period.

### Pressure in a Gas

Gas Pressure is created when gas particles collide with the walls of their container. The more often the particles collide with the walls, and the faster they are moving, the greater the pressure.

### Pressure in Fluids

Fluid pressure is exerted on the surface of an object in a liquid. This pressure causes upthrust . An object placed in a liquid will begin to sink. As it sinks, the liquid pressure on it increases and so the upthrust increases.

### Acceleration

Acceleration is how quickly the velocity is changing whether it be speed, direction or both. Acceleration is a measure of how quickly the velocity of an object is changing.

### Speed

Speed is how fast an object is moving in no given direction. Velocity is how fast an object is moving in a given direction. In physics, you can calculate the average speed by taking the total distance travelled and dividing it by the total time required to travel that distance.

### Weight on the Moon

Weight is the force acting on an object due to gravity. The weight of an object is defined as the force of gravity on the object and can be calculated as the mass times the acceleration due to gravity.

### Weight on Earth

Weight is the force acting on an object due to gravity. The weight of an object can be defined as the force of gravity on the object. Since the weight is a force, its unit is the Newton.
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