Physics #101: The Forces Implied in Kicking

The first mission of Stage 1 is a mission that is based on many science principles. Have you ever played soccer? If not, it’s a sport where you kick a ball to reach a goal. Sounds familiar?

So what is the science, or more specifically the physics, behind soccer? You will find that forces is one of the principles that you have probably learned from school by now. But just to recap:

• Force – a push or a pull, acting on an object as a result of its interaction with another object. It is a vector quantity which means that it has both magnitude and direction. There are two broad categories of forces: contact force and action-at-a-distance force.

Contact force is the type that result when two interacting objects are perceived to be physically contacting with each other. Examples are the following: Frictional force, Tensional force, Normal force, Air resistance force and Applied forces.

• Frictional force – The force exerted by a surface as an object moves across it or makes an effort to move across it.
• Tensional force – the force that is transmitted through a string, rope, cable or wire when it is pulled tight by forces acting from opposite ends.
• Normal force – the support force exerted upon an object that is in contact with another stable object
• Air resistance force – a special type of frictional force that acts upon objects as they travel through the air.
• Applied force – force that is applied to an object by a person or another object.

Action-at-a-distance force, on the other hand, are those types of forces that result even when the two interacting objects are not in physical contact with each other, yet are able to exert a push or pull despite their physical separation. Examples are Gravitational force, Electrical force and Magnetic force.

• Gravitational force – the force with which the earth, moon, or other massively large object attracts another object towards itself.
• Electrical force – the repulsive or attractive interaction between any two charged bodies 
• Magnetic force – attraction or repulsion that arises between electrically charged particles because of their motion.

Now, let’s see what forces are applied on soccer ball.

When the soccer ball is at rest, the only forces acting upon it are the gravitational force and normal force which are equal and opposite in direction. Since the forces are balanced, the object remains at rest.

Following the Newton’s First Law of Motion, the Law of Inertia, the object will stay at rest or uniform in motion unless acted upon by an unbalanced force. In other words, to make the ball move initially, an applied force which is the kick should be applied. How hard the person kicks the ball will dictate the initial velocity and the angle of the trajectory (curved path).

Now, all this is explained in the situation in which we have gravity. In the first mission though, things are a bit different: the gravitational force is missing! Complete the first mission of Stage 1 and, based on your experience, try to write down how does an object behave when kicked in an environment where there is no gravity.

Source: https://www.physicsclassroom.com