Dynamics/Kinetics:
Sir Isaac Newton
Newton's First Law of Motion states: "If the net force (total force) of an object is zero, the object will maintain its state of rest or uniform motion".
Newton's Second Law of Motion states: "The acceleration of an object is directly proportional to the magnitude of the net force and inversely proportional to the mass of the object".
Newton's Third Law of Motion states: "For every action force, there is an equal and opposite reaction force".
Newton's Second Law of Motion states: "The acceleration of an object is directly proportional to the magnitude of the net force and inversely proportional to the mass of the object".
Newton's Third Law of Motion states: "For every action force, there is an equal and opposite reaction force".
NEwton's First LAw of Motion:
In football, while a football is moving through the air with a constant velocity, either after being kicked or thrown, there will be air resistance which will make the football decelerate causing a projectile motion. Inertia is the resistance of an object to a change in its state of motion or rest. So a football will continue to move in uniform motion, or stay at rest until an unbalance force is acted upon the football. This can happen when a defender or an offensive player catches or deflects the ball in the opposite direction, or the football is stopped by the net after being kicked. This is how football relates to Newton's First Law of Motion.
NEWTon's Second Law of Motion:
The NFL (National Football League) and the CFL (Canadian Football League), both use different size footballs. In this example we will find out which football will have more acceleration. More importantly how would an athlete's performance in the NFL differ from an athlete's performance in the CFL? A NFL football has a mass of 0.400kg (400g) and a CFL football has a mass of 0.430kg (430g). If an equal force is applied to both types of football, the heavier one will not travel as far a distance and attain as high a velocity as the lighter football will. This relates to inertia, because the more mass an object has the more inertia it has. Therefore the acceleration is based on the equated Fnet = ma or a = Fnet/m. 'Fnet' is the total net force, 'm' is the mass of an object in grams and 'a' is the acceleration. In conclusion if the object has a greater mass/inertia, more force will be needed to increase the acceleration and if the object has a smaller mass/inertia, less force will be needed to increase the acceleration.
CFL Football:A CFL kicker kicks a CFL football that weighs 0.430kg with a force of 250N. What is the acceleration?
Fnet = ma Fnet = 250N m = 0.430kg a = ? 250 = 0.430a 250/0.430 = a a = 581.3953m/s squared (with significant digits the answer is 581m/s squared) Therefore the acceleration of the CFL football is 581m/s squared. | NFL Football:A NFL kicker kicks a NFL football that weighs 0.400kg with a force of 250N. What is the acceleration?
Fnet = ma Fnet = 250N m = 0.400kg a = ? 250 = 0.400a 250/0.400 = a a = 625m/s squared (with significant digits the answer is 600m/s squared) Therefore the acceleration of the NFL football is 600m/s squared. |
Since the CFL football has a slower acceleration than the NFL football after having the same force applied, we know the athletes in the CFL have a harder time of performing at a higher level.
Newton's Third Law of Motion:
Figure 1: Newton's Third Law of Motion
When a football is kicked by the kicker, the kicker might feel his foot vibrate a little at impact. This is how football relates to Newton's Third Law of Motion: for every action force, there is an equal and opposite reaction force. The action force is the kicker swinging his leg towards the football. The reaction force is the football pushing back on the kicker's foot in the opposite direction (figure 1). From the previous example we were able to determine the acceleration of a CFL football and a NFL football. We also know the force applied by the kicker on the football. What we don't know is the acceleration of the entire system, including the foot acceleration as well as the force acting on the foot by the football. To figure out these two things, we will use the formula Fnet = ma. For the mass of the kicker's foot we will use the mass of an average size male's foot (10) which is 1kg (1000g). We will also use the mass of the NFL football (400g).
Acceleration of the Foot:Fnet = ma
Fnet = 250N m = 0.400kg + 1kg = 1.4kg a = ? Fnet = ma 250 = 1.4a 250/1.4 = a a = 178.5714m/s squared (with significant digits the answer is 180m/s squared) Therefore the acceleration of the kicker's foot is 180m/s squared. | Force acting on the foot by the football:Fnet = ma
Fnet = Fapp (force applied) + Ft (tension force) Fapp = 250N Ft = ? m = 1kg a = 178.5714/s squared Fapp + Ft = ma 250 + Ft = (1) (178.5714) 250 + Ft = 178.5714 Ft = 178.5714 - 250 Ft = -71.4286N (with significant digist the answer is -71N) The answer is negative which means the force of the football is acting in the opposite direction in which the kicker is kicking the football. Therefore the force acting on the kicker's foot by the football is 71N (to the left). |
Science of NFL Football: Newton's First Law of Motion: http://science360.gov/obj/video/70fadaa8-c3d4-4132-ba1f-c98be5caeb14
Science of NFL Football: Newton's Second Law of Motion: http://science360.gov/obj/video/58e62534-e38d-430b-bfb1-c505e628a2d4
Science of NFL Football: Newton's Third Law of Motion: http://science360.gov/obj/video/d0e16d27-05d4-4511-9394-2758aa066981
Science of NFL Football: Newton's Second Law of Motion: http://science360.gov/obj/video/58e62534-e38d-430b-bfb1-c505e628a2d4
Science of NFL Football: Newton's Third Law of Motion: http://science360.gov/obj/video/d0e16d27-05d4-4511-9394-2758aa066981