(SF) Forces Lesson
Forces
Force plays a role in all aspects of our lives, from our trip to the store to simply walking across the floor. We are influenced by various forces that act upon us constantly, and understanding these forces can allow us to use them for our benefit. The most basic force that we encounter is gravity. It pulls on everything that has mass, and is one of the basic forces that control the universe.
A force is an influence that changes an object's motion, direction or geometrical arrangement. Simply put, any push or pull on an object is a force. Force is calculated by taking the mass of an object and multiplying it by the acceleration of the object. The resulting force is measured with a unit called the Newton.
Since this relationship was first described by Sir Isaac Newton, the unit is named in his honor. We now know this relationship as Newton's second law of motion and it can be expressed mathematically in the following expression.
Force = Mass x Acceleration
F = MA
Example Problem:
If an object has a mass of 100kg and it is accelerating at 20 m/s2 how much force does it generate?
F = MAF = 100 kg ×20 m / s2F = 200 kg ⋅m / s2or 100N
***Notice in the problem above, the units kg m/s2 are converted to N where 1 kg m/s2 = 1N***
Force in Sport
Forces play a vital role in sports. When an athlete performs any action, they are using forces. The play of the game, the amazing shots, the long touchdown pass and the home run that wins the game all have their foundation in forces. Forces are applied to an athlete's body, the equipment they use and the ball that is the center of the sporting event. Understanding forces is key to an athlete performing at their peak ability and giving them the competitive edge over their opponent.
Gravity
Let's look at a few forces a little closer to see their role in athletic events. Gravity is the greatest force that acts on a player during a sporting event. How high an athlete can jump, how far they can run, the trajectory of the ball, timing of a catch and many other movements are influenced by gravity. Gravity is a natural force that exists between two objects. Any object that has mass produces a gravitational field; this means that you are attracting everything around you as we speak! Why are objects not flying toward you? This is because your gravitational pull is too small to generate enough force to move an object. A planet on the other hand is very massive and therefore can generate forces far greater that you. Gravity constantly pulls down on all objects, and their motion is determined by its force.
Let's look at a quarterback throwing a ball as an example. The quarterback has to calculate how much force he needs to put on a ball in order to have the ball land in the receiver's hands. Gravity is used in the calculation because the ball will follow an arc pattern after it is thrown. The ball is thrown in both a vertical and horizontal direction so that the peak of the flight occurs exactly half way between the quarterback and the receiver. If the quarterback is off in his calculation, the ball may fall short or sail too far so that the receiver cannot make the play.
Weight
Gravity also determines the weight of an object. Weight is the mass of an object multiplied by the gravitational force exerted on that object. In sports we tend to look at an athlete's size and weight to determine the position that they are going to play. Gravity is pulling on the mass of the player toward the center of the Earth giving the player a force in the downward direction. A player with a large mass produces a greater downward force, so a 350lb lineman would be much harder to move than a 180lb receiver. This is the reason larger athletes play the position of lineman where movement is minimal, while smaller athletes play positions that rely on speed and large changes in position.
If we were to take our 350lb lineman and ship him to the moon he would only weigh around 58lbs! This is due to the difference in gravitational pull on the moon as compared to the Earth. The moon has 1/6 the mass of the Earth and therefore has 1/6 of the gravity of Earth. This is the reason astronauts seemed to float as they walked on the moon, they were very light compared to their weight on Earth.
Weight = Mass x Gravity
W = MG
The gravitational pull of the Earth is calculated to be 9.8 m/s2 and is used as a standard for calculations. If we use this value and multiply it by the mass of an object we can calculate its weight.
Example Problem:
An object has a mass of 250 kg. If we want to calculate its weight, we simply multiply the mass by the acceleration due to gravity.
Weight = Mass x Gravity
Weight = 250kg x 9.8 m/s2
Weight = 2450kg 
⋅ m/s2
OR 2450 N
Inertia
Inertia is another property of matter that plays a role in sporting events. Inertia is the tendency for an object to remain at rest or to remain in motion unless acted upon by an outside force. This is known as Newton's first law of motion . If a large player is standing in the way of another they are more difficult to move than if they are at rest. If they are already moving, they are much easier to displace. This applies to a running back in motion, too. He has a tendency to stay in motion. It is harder to bring down a player who is in full sprint. As you can see, this can apply to other sports as well. In baseball, the ball wants to remain in motion after it is hit by the batter. The fielder has to stop the ball's motion by using a padded glove to apply an opposite force to overcome the inertia of the ball.
Friction
Friction is an unusual force. Friction only occurs when another force is working in the opposite direction. Friction is the interaction between two objects that results from the small imperfections on the surface of the objects, that when in contact, adhere to each other. Some surfaces are very rough, while others are very smooth. This causes friction between objects to vary depending on how much they adhere to one another. In sports, friction plays a major role in many games. Hockey, for instance, relies on a surface that has a very low coefficient of friction. The coefficient of friction is the ratio between the force necessary to move one surface horizontally over another and the pressure between the two surfaces. The player's skates glide across the smooth surface of the ice allowing players to reach high speed. The hard rubber puck also glides freely across the surface allowing players to shoot the puck quickly at the goal in the hopes that it slides past the goalie before he can react. When the surface becomes too rough, a huge machine called a Zamboni comes onto the ice and smooths the surface again so that the players can play up to their optimum level.
Newton's Third Law of Motion
Other forces also play a role in sporting events. The force generated by a player when they hit a ball, tackle an opponent or kick a goal are used to cause changes in the position of people and objects as the game is played. These forces are unbalanced, which means that one force is stronger than another. When a ball is thrown, the force the athlete puts on the ball is stronger than the force in the opposite direction. This causes the ball to move in the direction of the stronger force. This follows Newton's third law of motion; for every action there is an equal and opposite reaction.
As you can see, there are many forces that are at work during a sporting event. From gravity, to the force applied by the athlete's muscles, forces are everywhere. Without forces nothing would happen; balls would sit still, players could not move and the game could not be played at all. The next time you watch a sporting event, think about all of the forces involved that make it possible and how they control the games we love.
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