SEHS 4.3..The Fundamentals of Biomechanics III

Define Newton’s three laws of motion• Newton's first law states that a body at rest will

remain at rest, and a body in motion will remain in motion with a constant velocity, unless acted upon by a force. This law is also called the law of inertia

• Newton's second law states that a force acting on a body is equal to the acceleration of that body times its mass. Expressed mathematically, F = ma, where F is the force in Newtons, m is the mass of the body in kilograms, and a is the acceleration in meters per second per second.

Cont’d• Newton's third law states that for every action

there is an equal and opposite reaction. Thus, if one body exerts a force F on a second body, the first body also undergoes a force of the same strength but in the opposite direction.

• Might want to know this one too…. the law of conservation of energy states that the total energy of an isolated system cannot change—it is said to be conserved over time. Energy can be neither created nor destroyed, but can change form; for instance, chemical energy can be converted to kinetic energy.

Explain how Newton’s three laws of motion apply to sporting activities

• 1st law--Basically, if an object is in motion, it keeps going unless something stops it. What are examples of outside forces that affect inertia? Most anything in the real world--gravity, the surface of the playing field, a defensive player, or the braking action of an athlete's body to stop.

Cont’d• 2nd Law -- If a baseball player hits a ball with double

the forceor with a bat of double the mass, the rate at which the ball will accelerate (speed up) will be doubled. Football players can slow down, stop, or reverse the direction of other players depending upon how much force they can generate and in which direction.

Cont’d• A swimmer propels herself through the water because the

water offers enough counterforce to oppose the action of her hands pushing, allowing her to move. An athlete can jump higher off a solid surface because it opposes his body with as much force as he is able to generate, in contrast to sand or other unstable surface.

State the relationship between angular momentum, moment of inertia and angular velocity

• Angular momentum (L)- is a vector quantity that represents the product of a body's moment of inertia (I) (i.e., a measure of an object's resistance to changes in its rotation velocity) and angular velocity (w) about a particular axis.

•L = Iw

Explain the concept of angular momentum in relation to sporting activities

• Most applicable to dance, figure skating (twisting jump and spins) and diving.

• Angular momentum is conserved when no outside torques act on an object. For example, as the moment of inertia decreases, the angular rotation has to increase to keep the same angular momentum. This is most evident when a figure skater spins. A skater starts the spin with arms outstretched (a large moment of inertia). As the skater brings the arms in (decreasing the moment of inertia), the rotational speed increases. This is how those incredible spins skaters are accomplished.

• https://www.youtube.com/watch?v=dUq8-5nwHOU

Cont’d

• Rotational disc/stool/chair with dumbbells demo

• https://www.youtube.com/watch?v=UZlW1a63KZs&list=PLD5CDF2754D03A326&index=3

Explain the factors that affect projectile motion at take-off or release

*Many sports involve the projection of an object into the air e.g shot put, soccer, tennis.

*This also applies to the human body e.g gymnastics, long jump, high jump.

*The quality of performance depends very largely on the performers ability to control the projectile.

Cont’d• A projectile is any body that is given initial velocity

(speed) and follows a path determined by the affect of gravity and air resistance.

• The path followed by a projectile is called a trajectory.

• The projectile is affected by horizontal and vertical motion, which are independent of each other.

• You can use information such as speed of release and angle of release to calculate how far the object will travel.

Cont’d• There are three factors that affect projectile motion:• Angle of release

• Height of release

• Speed of release

• You can change each of these three factors to influence the distance.

Outline the Bernouli principle with respect to projectile motion in sporting activities

• First…What is the Bernoulli principle?

• Bernoulli's principle, sometimes known as Bernoulli's equation, holds that for fluids in an ideal state, pressure and density are inversely related: in other words, a slow-moving fluid exerts more pressure than a fast-moving fluid. Since "fluid" in this context applies equally to liquids and gases, the principle has as many applications with regard to airflow as to the flow of liquids.

Cont’d – Be able to explain two sports examples of the Bernoulli Principle

• A golf ball’s flight:

• Given the proper spin a golf ball can produce lift. Originally, golfers thought that all spin was detrimental. However, in 1877, British scientist P.G. Tait learned that a ball, driven with a spin about a horizontal axis with the top of the ball coming toward the golfer produces a lifting force. This type of spin is known as a backspin. The backspin increases the speed on the upper surface of the ball while decreasing the speed on the lower surface.

• Results in the Magnus Effect: http://www.youtube.com/watch?v=23f1jvGUWJs

Cont’d – Baseball and Cricket examples

• http://www.youtube.com/watch?annotation_id=annotation_859181&feature=iv&src_vid=23f1jvGUWJs&v=t-3jnOIJg4k