#### Transcript Linear Motion

```Biomechanics
• Mechanics of movement:
– vectors and scalars – velocity, acceleration and
momentum/impulse in sprinting
– Newton’s Laws applied to movements –
application of forces in sporting activities
– projectile motion – factors affecting distance,
vector components of parabolic flight
– angular motion – conservation of angular
momentum during flight, moment of inertia
and its relationship with angular velocity.
Using ‘Newton’s First’ and ‘Second Laws of Motion’, explain how
the swimmer dives off the starting blocks. (4 marks)
4 marks for 4 of:
• A. Force is applied by the muscles
Newton’s First Law of Motion/Law of inertia
• B. Performer will remain on the blocks unless a force is applied
• C. Performer continues to move forwards with constant velocity
until another force is applied
• D. Water slows the swimmer
Newton’s Second Law of Motion/Law of Acceleration
• E. Mass of swimmer is constant
• F. Greater the force exerted on the blocks, the greater the
acceleration/momentum
• G. Force governs direction
(something WILL come up on this subject!)
Biomechanics
The term ‘Biomechanics’ literally means ‘the mechanics of
living beings’ and it is used to analyse human performance
from a scientific standpoint with the aim of:
• achieving optimal sporting techniques,
• improving the design of equipment
• determining the stresses imposed on the body during
performance in order to prevent injury.
Linear Motion
• Occurs when a body moves in a straight or curved line
with all parts of the body moving the same distance in
the same direction at the same speed.
• We are going to cover the following aspects of linear
motion:
Vectors
Speed
Acceleration
Scalars
Velocity
Force
Mass
Distance
Inertia
Weight
Displacement
Momentum
Vectors and scalars
Scalar Quantities – are only considered in terms of their
magnitude
Vector Quantities – are considered in terms of magnitude
and direction
E.g. a man is walking at 2km/h = ??
Scalar
A man is walking north-east at 2km/h = ?? Vector
Mass and Weight
Mass
– is the amount of matter (‘stuff’) that something
Scalar
It is measured in Kg
Weight
– Is the force exerted on the mass of a body by
gravity.
Vector
It is measured in Newtons (N)
Weight = mass x acceleration due to gravity
On Earth, acceleration due to gravity is ~ 10 m/s2…
Are mass and weight scalar or vector quantities?
… so weight is 10x mass!
Force
Force is the ‘push or pull’ exerted on an object or body,
which may either cause motion of a stationary body or a
speeding up, slowing down or change of direction of a
moving body.
Force can be generated internally by Muscle contraction or
externally by Gravity, friction, water and air resistance
Without such forces, movement would not be possible, and
when such forces are understood and adapted to the same
aim, optimal performance can be achieved.
Force is a Vector quantity – what does this mean?
It has magnitude and direction.
Often, more than one force is acting upon an object.
The resultant force can be calculated by either adding the
forces in the same direction; subtracting the forces in
opposite directions, or by constructing a parallelogram of
forces with the resultant force lying on the diagonal of the
parallelogram.
Draw arrows to show the resultant force from the following
vectors:
a)
d)
b)
e)
c)
f)
Linear Motion
• Occurs when a body moves in a straight or curved line
with all parts of the body moving the same distance in
the same direction at the same speed.
• We are going to cover the following aspects of linear
motion:
Vectors
Speed
Acceleration
Scalars
Velocity
Force
Mass
Distance
Inertia
Weight
Displacement
Momentum
Speed and Velocity
When analysing sporting performance, we are always
concerned with how fast a body or an object is – i.e.
their speed
Is speed a scalar or
vector quantity?
Distance travelled (m)
Speed =
Scalar
Time taken (s)
1. Calculate the speed (m/s) of a person who jogged 600m
in 2 minutes
2. Calculate the distance (m) a man would travel in 3
minutes running at a speed of 4 m/s
3. Calculate the time it would take a woman to swim 400m
at a speed of 1.6m/s
1. Calculate the speed (m/s) of a person who jogged
600m in 2 minutes
Speed = D/T = 600 / 2x60 = 600 / 120 = 5m/s
2. Calculate the distance (m) a man would travel in 3
minutes running at a speed of 4 m/s
Distance = SxT = 4 x (3x60) = 4 x 180 = 720m
3. Calculate the time it would take a woman to swim
400m at a speed of 1.6m/s
Time = D / S = 400 / 1.6 = 250s
Speed and Velocity
Velocity is a Vector quantity – what must it have that
Direction
speed doesn’t?
Velocity =
Displacement (m)
Time taken (s)
Displacement is the shortest possible route between the
starting and finishing point – normally measured in a
straight line (as the crow flies) in metres (m)
As velocity is a vector, directional information is needed
to fully describe it.
i.e the car travelled with a velocity of 30mph in a
south-westerly direction.
Look at page 82 of the textbook to see the distance and
displacement of the great north run compared.
Acceleration (and deceleration)
Is acceleration a
scalar or vector
quantity?
Vector
I.e. it is the rate of change of velocity of an object.
-1)
Change
in
Velocity
(ms
Acceleration =
Time (s)
We tend to think of it as how quickly an object is
speeding up, or slowing down.
Acceleration should be stated with a direction
e.g. the sprinted accelerated at 5ms-2 towards the
finish line
The high jumper accelerated upwards at 8ms-2
The Acceleration (or deceleration) of an object can be
shown through the gradient of a velocity-time graph.
Figure 2 shows a velocity/time graph for an elite 100-metre sprinter.
(i) Use Figure 2 to determine the velocity of the sprinter after 3
seconds, and identify the period of time when the sprinter’s acceleration
was the greatest.
(2 marks)
(ii) What is happening to the sprinter between 6 and 11 seconds? Explain
why this occurs.
(3 marks)
(b)
(i)
1. 9.1 ms-1 (accept 9.0-9.2);
2. 0-1 seconds.
2 marks
(ii) 1. Deceleration/decrease in velocity; (Do not
credit slowing down)
2. Lack of ATP;
3. CP breakdown to ATP slowing/limiting;
4. Due to lack of stored PC;
5. Change to slower lactic acid/
alactic/anaerobic system
3 marks
Linear Motion
• Occurs when a body moves in a straight or curved line
with all parts of the body moving the same distance in
the same direction at the same speed.
• We are going to cover the following aspects of linear
motion:
Vectors
Speed
Acceleration
Scalars
Velocity
Force
Mass
Distance
Inertia
Weight
Displacement
Momentum
Inertia
• Inertia is the reluctance of a body to move or change
its state of motion
• Objects will stay in their state of inertia (i.e.
stationary or moving at a constant velocity) unless a
force overcomes that inertia.
•The inertia of a body is
directly proportional to its mass
• Therefore an object with a
greater mass requires a larger
force to overcome its inertia
and change its state of motion.
Momentum
• Momentum is the amount of motion a body has
• Momentum is calculated as:
Mo = Mass (kg) x Velocity (ms-1)
• The more massive, or the faster an object, the more
momentum it has.
• Momentum is linked to inertia – the more momentum
something has, the harder it is to stop!
Ben Morgan
1m 93
117 kg
Leigh
Halfpenny
Richie Gray
2m 08cm
120 kg
1m 78cm
83 kg What is each of
their momemtum
when running at
4ms-1
Prep
Definitions sheet