3.1 - Newtons laws, force and use of tech

Newtons 2nd Law of acceleration

Newtons 3rd Law of reaction

Newtons 1st Law of inertia

a body continues in a state of rest or uniform velocity unless acted upon by an external or unbalanced force

example = a 100m sprinter in the blocks will want to stay at rest in the blocks until an external force large enough to overcome their inertia creates motion. Equally, when the sprinter reaches a constant velocity, they should continue at that constant velocity until an external or unbalanced force acts upon it.

a body's rate of change in momentum is proportional to the size of the force applied and acts in the same direction as the force applied

example - the greater the force applied to the sprinter, the greater rate of change in momentum and therefore acceleration away from the blocks. The force is applied in a forward direction and so the sprinter drives towards the line.

for every action force applied to a body there is an equal and opposite reaction force

example - when the 100m sprinter applies a down and backward action force into the blocks, the blocks provide an equal and opposite up and forward reaction force to the sprinter to drive them out of the blocks

Limb kinematics

Force plates

Wind tunnels

  • a 3D motion analysis records an athlete performing a sporting action or a patient performing normal body movements
  • allows joint and limb efficiency to be evaluated with measurements of multiple planes of movement
  • computer software and infra-red cameras record the motion shown by the reflective markers that are placed on the bodies joints

advantages

disadvantages

  • data is produced immediately and is objective and accurate
    • coaches can use this to help improve performance and adjust technique
  • it can focus on specific joint movement and analyse technique
  • the accuracy and repeatability of the results depends on the correct placement of the markers on the body
  • it is highly specialised
  • very expensive
  • very limited to lab conditions which makes some actions difficult to perform in those environments

  • used to assess the aerodynamics


  • objects are placed inside the wind tunnel and instruments are attached to measure forces produced by the air against it's surface

  • used to study the flow of air
  • a rectangular metal plate inserted into the ground at the take off area of a long jump or high jump or in a track after a sprint start
  • information produced can tell a person the precise way in which the foot is active during its strike with the ground
  • when contact is made, an electrical output proportional to the force being applied is displayed on a computer in a graphical form

Force

Internal force = generated by the contraction of a skeletal muscle

External force = comes from outside the body and acts upon it

  • weight, reaction, friction and air resistance

5 effects:
1) can create motion = football will remain at rest until a force applied to make it move
2) can accelerate a body = greater force applied by the foot to the ball, greater acceleration of ball to goal
3) decelerate a body = ball moves through air, force of air resistance will act in opposite direction
4) change direction of a body = goalkeeper dives to save a shot, force from hands will change direction of ball away from goal
5) change shape of body = goalkeeper fails to save shot, ball hits the net and net changes shape

Net force

the sum of all forces acting on a body, resultant force. the overall force acting on a body when all individual forces have been considered

  • if a net force = 0, there is no change in motion as the forces are balanced
  • a body will remain at rest or will continue to travel at constant velocity
  • if a net force is present, there will be a change in motion as the forces are unbalanced
  • a body will accelerate, decelerate, change its direction or change shape

Vertical forces

Calculations

acceleration = final velocity - initial velocity / time taken

momentum = mass x velocity

velocity = displacement / time taken

force = mass x acceleration

Weight = mass x acceleration due to gravity

Reaction = equal and opposite force exerted by a body in response to the action force placed upon it

Horizontal forces

Friction = the force that opposes the motion of two surfaces in contact

Air resistance = the force that opposes the motion through the air

Free body diagram

a clearly labelled sketch showing all of the forces acting on a body at a particular instant in time

examples = runners or cyclists

Vertical forces:

  • Weight = from the centre of mass extending vertically downwards
  • Reaction = from the point of contact extending vertically upwards

Horizontal forces:

  • Friction = from the point of contact and usually extending horizontally in the same direction as motion
  • Air resistance = from the centre of mass and extending horizontally against the direction of motion

Advantages

Disadvantages

  • uses very specialised facilities that are only in engineering bases
  • they are very expensive
  • require complex analysis by research professionals
  • decreases air resistance by up to 7% in F1 cars
  • allows engineers to have tight control on environmental variables
  • increases accuracy of aerodynamic objects

Advantages

Disadvantages

  • used for biomechanical assessment, analysis of posture and human motion, balance, rehabilitation and physical therapy
  • gives immediate, accurate and reliable results
  • an expensive and specialist piece of equipment
  • mainly used in laboratory conditions