1 a2 revision mechanics of movement. 2 biomechanics terms: displacement; velocity; acceleration
Post on 18-Jan-2018
228 Views
Preview:
DESCRIPTION
TRANSCRIPT
1
A2 Revision
Mechanics of movement
2
Biomechanics
Terms:• Displacement;• Velocity;• Acceleration
3
Displacement or Distance
AB
Length of journey in meters =
Straight line from start to finish in meters =
distance
displacement
4
Displacement and velocity
• Velocity • Displacement and velocity have direction
displacement divided by time
5
Velocity/time graphs – 100-m
Velocity
Time
Velocity changes
6
Change in velocity
• Average velocity changes
• Change in velocity over a period of time is called
Acceleration =
acceleration
final velocity – initial velocity
time taken
7
Velocity
Time
On a velocity-time graph acceleration is shown by the
of the line
steepness (gradient)
8
Velocity
Time
Highest acceleration?
zero acceleration?
deceleration?
9
Vectors and scalars
• Displacement, velocity and acceleration have direction as well as magnitude =
• Temperature, time, speed, etc do not have direction =
vectors
scalars
Typical Question
Explain, in terms of the player moving towards a ball, the difference between velocity and acceleration. (3 marks)
Answer
1. Velocity = rate of change of displacement/displacement ÷ time;
2. How fast/quickly player moves towards ball;3. Acceleration (not speed) = rate of change of
velocity/change in velocity ÷ time (taken to change)/[Vf - Vi] ÷ time/a = v ÷ t;
4. Push off ground to accelerate (not speed)/change velocity;
5. (Both) have direction/are vectors.
12
Forces
Forces cause ; A force is a
“A force is that which alters or to alter a body’s or of in a line.”
If a body changes or , a has been applied
force
movementpush or a pull
tendsstate of rest
uniform motion straight
direction velocity
13
Forces affecting motion
• Action/muscular forces• Reaction forces• Gravity• Air resistance/friction
14
Forces acting on a sprinter
Action force of muscular contraction
Friction
Gravity
Air resistance
Equal and opposite Ground Reaction Force
15
Forces applied - runner
• forces applied to ground• Reaction force from• • between ground and foot• Air resistance
Muscularground
GravityFriction
to forward motion
Typical question
What forces act on a player when they are running during a game? (3 marks)
Answer
1. Gravity;2. Friction;3. Air resistance;4. Action force/muscular forces;5. Reaction forces/ground reaction force;
18
Newton’s Laws
• 1st Law –
• A body will remain in its / until affected by a
• A body has a to change its
Law of inertia
state of motion
reluctance
rest force
state of motion
19
Applying Newton’s 1st Law
• Sprinter remains in on blocks until a causes him to change his
• Ball keeps moving until a causes it to change its
force
set positionforce
state of motion
state of motion
20
Momentum
• In sporting situations, remains constant; therefore inertia
• All objects in motion have mass and
• Product = • Momentum =
massstays the same
velocity
momentumquantity of motion
21
Newton’s Laws
• 2nd Law –
• The rate of change of is to the force causing the change, and the change takes place in the in which the force was applied • In sport, remains constant and therefore momentum equates to
Law of acceleration
momentumdirectly proportional
directionmass
acceleration
22
Applying Newton’s 2nd Law
• The (size) and of force applied by the sprinter to the blocks determines the and of received – because mass remains constant• Acceleration is to applied•
magnitude direction
magnitude directionacceleration
proportional force
F ∞ a
23
Newton’s Laws
• 3rd Law – Law of Reaction
• To every force there is an and reaction force
equalopposite
24
Applying Newton’s 3rd Law
• The sprinter applies a to the ground. This results in a force causing movement
• The sprinter cannot move the
• Reaction force from ground =
muscular forcereaction
earth/blocks
Ground Reaction Force
Typical question
Use Newton’s Laws of motion to explain how a sprinter leaves the starting blocks. (6 marks)
Answer1. Newton’s First law – a body remains in a state of motion until acted
upon by a force;2. Sprinter remains stationary until a force causes them to change their
state of motion/overcome their inertia; 3. Newton’s Second Law- body accelerates/changes momentum with a
magnitude that depends on magnitude of force causing change (nb not F=ma);
4. Also force gives direction;5. Sprinter applies force to ground;6. Magnitude of muscular force determines acceleration given to sprinter;7. Newton’s Third Law – to every force there is an equal and opposite
reaction force;8. Action/applied force are muscular contractions given to earth;9. Equal and opposite reaction force moves the lighter mass of the
sprinter;
27
Projectile motion
•Flightpath = parabola
28
Components
• Motion of projectile has components• component• component
two
VerticalHorizontal
29
Projectile motion
Vertical motion is affected by gravity –
Horizontal motion is affected by friction –
Vertical component
Horizontal component
continually decreasing
usually negligible
30
Variations in vertical and horizontal components
This causes the observed parabolic flight and affects the motion components as follows:
31
Projectile motion
Factors affecting distance travelled:• • •
Speed of release Height of release Angle of release
Typical question
Elite golfers use their clubs to overcome the forces acting on the golf ball so that it travels long distances.(i)Describe how the impact of the golf club, gravity
and air resistance affect the velocity and acceleration of a golf ball. (4 marks)
(ii)The flight of a golf ball is said to be parabolic. Explain the term parabolic and the main factors that limit the distance that a golf ball will travel in flight. (4 marks)
Answer(i)1. Golf club - Applies force2. Gives acceleration/changes momentum3. Gravity - Only affects vertical component of flight4. Reduces/negative effect on velocity/ decelerates5. Air resistance - Affects both vertical and horizontal components6. Reduces/negative effect on velocity/ decelerates(ii)7. Left and right sides match/mirror each other8. Height of release – higher height above landing more distance9. Angle of release – closer to 45° the better10. Speed of release – more force more speed more distance
Factors affecting the fight of a parabola
• Velocity of Release- increase in speed of release = increase in displacement of projectile.
• Height of Release- increase in release height= increase in displacement of projectile.
Angle of Release
1) Release height= landing heightLofted pass in footy= 45 degrees2) Release height> landing heightShot put= < 45 degrees3) Release height< landing heightBunker shot in golf >45 degrees
36
Impulse
• • Measured during – force
platforms on track• Displayed as
Force x time
sprinting
Force.time graph
37
timeforce
negative
positive
• Impulse = force x time• shown as area under graph
38
• Impulse is mainly concerned with
• Involves • Two parts
single events – a footfallhorizontal forces only
to a footfalllanding – negative horizontal forces
Push-off – positive horizontal forces
39
Typically
timeforce
neg
pos
Landing - negative impulse
Push-off - positive impulse
Net impulse is difference between positive and negative impulses
40
Typically
timeforce
neg
pos
Small negative impulse
Large positive impulse
Net impulse is positive – performer is accelerating
41
Typically
timeforce
neg
pos
Large negative impulse
Small positive impulse
Net impulse is negative – performer is decelerating
Typical question
(i)As a sprinter accelerates along the track at the beginning of a race, they generate a large impulse. What do you understand by the term impulse? (2 marks)
(ii)Sketch and label a graph to show the typical impulse generated by the sprinter at this stage of a race. (6 marks)
Answer(i)1. Impulse is force x time/force applied in unit of time;2. Equates to change in momentum;3. If mass constant equates to change in acceleration;(ii)4. Positive clearly larger than negative;5. x axis – time;6. y axis - force;7. Units of force shown as Newtons;8. Units of time shown as milliseconds/less than 1 second9. Time intersecting at zero on force axes;10. Positive and negative force axes labelled;11. Shape of graph - negative and positive components of force shown with
negative first;12. Negative and positive components of force labelled;
44
Angular motion
• During free rotation – remains constant
angular momentum
• This situation occurs when and during flight and during ice-skating (ignore friction)
somersaulting spinning
45
• Angular momentum is the
• Angular momentum =
• Angular velocity =
• Moment of inertia =
Angular Momentum
quantity of rotation
angular velocity x moment of inertia
rate of rotation or spin
spread of body’s mass
46
Constant angular momentum
• If you change the moment of inertia; then the also changes
• Tuck body up small to moment of inertia and angular velocity
• Seen during and
angular velocity
lowerincrease
somersaultsice-skating spins
Typical question
Explain the mechanical principles that allow spinning ice-skaters to adjust their rate of spin.
(6 marks)
Answer1. Ice may be regarded as a friction free surface/friction is
negligible;2. During spins angular momentum remains constant;3. Angular momentum is the quantity of rotation;4. Angular momentum = angular velocity x moment of inertia;5. Angular velocity = rate of spin/how fast skater spins;6. Moment of inertia = distribution/spread of mass around axis;7. Changing/reducing moment of inertia affects/increases
angular velocity;8. Skater brings arms into body allowing rate of spin to increase;
top related