I) Newton’s Three Laws of Linear Motion:

A) 1st Law: An object at rest has a tendency to remain at rest  and an object in constant motion tends to remain in  constant motion and to travel in a straight line with  uniform speed unless acted on by some net external force.

               1) Also known as the law of inertia.
               2) Inertia is a body's resistance to change its state of rest or uniform motion.
               3) Net force = Applied force - Resistive force.
                  -An object will move when the applied force is greater than the resistive force.
                  -Positive work and positive acceleration are produced when the applied forces are greater than the resistive forces.
                  -Negative work and negative acceleration are produced when the resistive forces are greater than the           applied  forces.
                  -Zero work is produced when the resistive and  applied forces are equal.
                  -Surface friction, gravity, air and water
                   resistance are all examples of resistive
                   forces.
 
 B) 2nd Law: When a body is acted upon by a net force, the  resulting acceleration (a) is directly proportional to the net force, and inversely proportional to the mass of the object, and takes place in the direction of the acting net force.
               1) Also known as the law of acceleration.
               2) Formula form: a = net Force/mass.
               3) Also, the relationships among the applied force,
                  a body’s mass, and the resulting acceleration
                  of the body has been expressed as

                          Force = mass x acceleration
 

C) 3rd Law: For every action force there is an equal and opposite reaction force.
              - Also known as the Law of Reaction.

Practical Applications of Newton’s Laws of Linear Motion.

1. Many of the fundamental relationships that form the foundation of modern mechanics were formulated by Sir Isaac Newton (1642-1727).
2. Newton’s first law of linear motion suggests that the more inertia an object has, the harder it is to change its state of motion; also, it is harder to start it moving from rest.
Practical application:
1. For human movement to occur, inertia must be changed.
2. During locomotion it is important to minimize the total external   resistance in order to keep the body’s inertia low.
3. The second law of linear motion expresses the interrelationships among force, mass and acceleration.

Practical application:
1. When a ball is kicked, thrown, or struck with an implement, it will travel in the direction of the line of action of the applied force. Also, the greater the applied force, the greater the speed of the ball.
2. Acceleration during human locomotion is directly proportional to the muscular force causing the acceleration. Therefore, the greater the propelling power (muscular force/time) the greater the acceleration of the body.
3. Newton’s third law, Law of Reaction, suggests that when one body exerts a force on a second, the second body exerts a reaction force that is equal in magnitude and opposite in direction on the first body.

Practical application:
1.Ground reaction forces are sustained with every footstrike (walking, running). Also, water reaction forces are sustained with every hand “push” (swimming). It is important that the direction of the action force is applied in such a way that the reaction force propels the body in the desired direction.
2.An 80 kilogram hockey player collides head-on with a 70 kilogram hockey player.  If the first player exerts a force of 400 Newtons in a positive direction (+) on the second player, how much force is exerted by the second player on the first?  Answer.  According to Newton’s third law, the second hockey player exerts an equal (400Newtons) and opposite force (-) on the first hockey player.
3. Propelling force for running is provided by the upward and forward ground reaction force in response to the downward and backward drive of the foot and leg. It is important to minimize the vertical component of this force in order to maximize the horizontal component. Less vertical component translates into less vertical movements of the center of gravity and therefore very little bounce in the running gate. An efficient running gate is one with little bounce.
 

Kinesiology   Newton’s Laws of Linear Motion
Newton’s Laws Applied to  Linear Motion: Study  Questions
 

1) An applied force greater than the resistive force will produce positive, negative, zero work?
 

2) An objects’s resistance to change its state of constant motion and/or rest (stationary ) is  called                 .
 

3) Would a person's weight be different or the same on the moon?
              .    Equation for weight                    .
 
 

4) Newton’s Second Law.
A. State Newton’s second law of linear motion in text and equation
   form.
 
 
 

B.  Impulse-Momentum Equation

From this law derive the impulse-momentum equation
Clearly define each component of the equation
 
 

And, explain how the impulse-momentum equation is related to  understanding locomotor “efficiency”. Show all work

5) Given that a box weights 980 Newtons, how much force must I apply to the box in an upward direction before positive work is  done?
 

6)Using the 980 Newton (N) box one more time, if I apply 1225 N  of force in the upward direction, what will be the net Force?
 

7) If an individual has a mass of 75 kilograms, what is his weight?
   Express weight as Newtons  and pounds
   Show all your work (calculations).
       Newtons                   Pounds
 

8) Using the 75-kilogram person again, what would his mass be on   the moon?
 

9) Why is it that humans cannot walk effectively (and technically, not at all) on a frictionless surface?
 
 
10) A body in a state of zero acceleration is at rest or in motion?
    Explain.