Portuguese footballing sensation, **Cristiano Ronaldo** has many gifts as a player. One of them is his ability to strike a football with immense power and speed.

In physics, Ronaldo’s ability can be measured and calculated. Power and speed are defined by the word **momentum**. We can use a formula to determine how much momentum Ronaldo can give to ball when he kicks it.

Discover one of the most important equations in physics with Cristiano’s help and see how easy it is to understand the motion of objects.

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## Test: Mass and Velocity

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## Cristiano Ronaldo

Portuguese footballer **Cristiano Ronaldo dos Santos Aveiro** was born in February 1985. He currently plays for Italian Serie A club Juventus and is captain of Portugal’s national team. Widely thought of as one of the greatest players of all time, Ronaldo has won five Ballon’s D’Or and 29 trophies, including six league titles, five UEFA Champions Leagues, one UEFA European Championship, and one UEFA Nations League. A prolific goalscorer, Ronaldo is one of the few players to have made over 1,000 career appearances and has scored over 700 goals for club and country.

Born and raised in Madeira, he is regarded as one of the most famous athletes in the world. Ronaldo also has the most followed accounts on both Instagram and Facebook. With earnings of £615 million from 2010 to 2019, he was ranked second in Forbes’ list of Highest Paid Athletes of the Decade behind boxer, Floyd Mayweather.

## Velocity

The velocity of an object is the rate of change of its position over time in terms of a specific frame of reference. In other words, an object's speed, and direction of motion. For example, 30 mph to the south.

Put simply, velocity is the speed at which something moves in one direction. The speed of a car traveling west on a motorway and the speed of a space shuttle moving through space can both be measured using velocity.

The SI (international) units for velocity are m/s (metres per second), but velocity may also be expressed in any units of distance per time. Other units include miles per hour (mph), kilometres per hour (kph), and kilometres per second (km/s).

Speed, velocity, and acceleration are all related, though they represent different measurements.

**Speed**is a scalar quantity that indicates the rate of motion distance per time. Its units are length and time. Thus, speed is a measure of distance travelled over a certain amount of time. Speed is often described simply as the distance travelled per unit of time. It is how fast an object is moving.**Velocity**is a vector quantity that indicates displacement, time, and direction. Unlike speed, velocity measures*displacement,*a vector quantity showing the difference between an object's final and initial positions. Speed measures distance, a scalar quantity that measures the total length of an object's path.**Acceleration**is defined as a vector quantity that indicates the rate of change of velocity. Acceleration is often referred to as ‘speeding up’, but it really measures changes in velocity. Acceleration can be experienced every day in a vehicle.

## Mass

Mass is a scientific term used to describe the density of any given object. The SI Unit of mass is the kilogramme (kg), though mass can also be measured in pounds (lb).

We use the word mass to talk about how much matter there is in something. On Earth, we weigh things to determine how much mass there is. The more matter there is, the more something will weigh. Often, the mass of an object is related to its size, but not always. A large balloon the size of your head will have far less matter inside it than your head and therefore less mass.

The difference between mass and weight is that weight is determined by gravity. If we compare two different things to each other on Earth, they are both pulled in the same way by gravity and so the one with more mass weighs more. But in space, where the pull of gravity is very weak, something can have almost no weight. However, it still has matter in it, so it still has mass.

If you landed on the moon and weighed yourself there, you would weigh more than you weighed in space but less than you weighed on Earth. If you continued your journey to the surface of Jupiter, you would weigh a great deal more. If you weighed 100 pounds on Earth you would weigh 16 pounds on the moon, 37.7 pounds on Mars, and 236.4 pounds on Jupiter. Yet, throughout your journey, your mass would remain essentially the same.

## Momentum

A moving object has momentum. This is the tendency of the object to keep moving in the same direction. It is difficult to change the direction of movement of an object with a lot of momentum.

Momentum is a derived quantity, calculated by multiplying the mass, *m* (a scalar quantity), times velocity, *v* (a vector quantity). This means that the momentum has a direction and that direction is always the same direction as the velocity of an object's motion. The variable used to represent momentum is *p*. The equation to calculate momentum is shown below.

Momentum can be calculated using this equation: **p = m × v**, where: **m** is the mass in kilogrammes kg, **v** is the velocity in metres/s and where **p** is the momentum in kilogrammes metres per second, kg m/s.

For example, the momentum of a 5 kg object moving with a velocity of 2 m/s is: 5 × 2 = **10 **kg m/s

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