4. 1 - Linear Motion Flashcards
what is a scalar quantity?
when measurements are described in terms of size/ magnitude
give examples of scalars.
mass
distance
speed
what is a vector quantity?
when measurements are described in terms of size/magnitude and direction
give examples of vectors.
weight
acceleration
displacement
velocity
momentum
how are vectors drawn?
using arrows
- length of arrow = magnitude
(longer the arrow, bigger the size)
- direction is shown by line of application, point of application and arrow head
define mass
the quantity of matter the body possesses
(Kg)
scalar
define weight
the gravitational force exerted on a given mass due to gravity
(N - newtons)
vector (it has size and direction - acting downwards from the centre of mass)
how do you calculate weight?
Mass (kg) x Gravity (9.8) = Weight (N)
define distance.
the path a body takes as it moves from the starting to the finishing position
(metres)
scalar
what do distance and displacement describe?
the extent of a body’s motion
- they tell us how far a body has travelled
define displacement.
the shortest route in a straight line between the starting and finishing position
(metres)
vector
define speed
the rate of change of distance
(m/s)
scalar
how is speed calculated?
speed (m/s) = Distance (m) / Time (s)
define velocity.
is the rate of change of displacement
(m/s)
vector
how is velocity calculated?
velocity (m/s) = displacement (m) / Time (s)
what does a straight flat line show on a distance time graph?
no distance travelled
- performer is stationary
e.g: netballer taking a shot
what does a straight diagonal line mean on a distance time graph?
line is constant
- the performer is travelling at the same speed
- distance run is changing at a constant rate
e.g: middle of a long distance race
what does a curved line that gradually gets steeper mean on a distance time graph?
more distance is being covered in a certain amount of time
- the performer must be accelerating
e.g: 20m at the start of a 100m race
what does a curved line that is steep but starts to level off mean on a distance time graph?
less distance is travelled in a certain amount of time
- deceleration is occurring
e.g: when the performer crosses the finish line
how do you calculate the gradient of a graph?
change in y axis / change in x axis
what does a straight flat line mean on a velocity time graph?
gradient is constant
- performer is travelling at a constant velocity
what does a curved line that gets steeper mean on a velocity time graph?
the gradient increases (it gets steeper)
- performer is accelerating (or moving with increasing velocity)
how would you find the gradient of a velocity time graph?
change in velocity / time
what does a curved line that decreases mean on a velocity time graph?
gradient decreases
- performer is decelerating (or moving with a decreasing velocity)
what does it mean if the line goes below the x axis on a velocity time graph?
there has been a change in direction
define acceleration.
the rate of change of velocity
(m/s^-2) or (m/s/s)
vector
what happens to acceleration when velocity increases or decreases?
increase in velocity: positive acceleration
decrease in velocity: negative acceleration
how do you calculate acceleration?
acceleration (m/s/s) = change in velocity (m/s) / time (s)
how do you calculate the change in velocity?
change in velocity = final velocity - initial velocity / time
what is momentum?
the product of the mass and velocity of an object
(kgm/s)
vector
how do you calculate momentum?
momentum (kgm/s) = mass (kg) x velocity (m/s)
can momentum be conserved?
yes
- occurs when a performer or object is in flight
- neither mass or velocity can be altered
what affects the conservation of momentum?
by an external force
e.g: gravity
what are the 2 types of force?
internal
external
these forces act upon a performer during linear motion
what is an internal force?
generated by skeletal muscles
e.g: force generated as the quadriceps contract concentrically to extend the knee in a jump
what is an external force?
comes from outside the body.
e.g: friction, air resistance, weight and gravity
give examples of external vertical forces.
gravity
weight
reaction force
give examples of external horizontal forces.
friction
air resistance
what is weight?
gravitational force that the earth exerts on a body, pulling it downwards
- greater the mass, greater the weight force pulling the body downwards
what is the reaction force?
this occurs when two bodies are in contact with one another
- the reaction force is at every point of contact
- whatever the force acting on a performer during linear motion, a reaction force will be generated
-Newton’s 3rd law(for every action force there is an equal and opposite reaction force)
apply the reaction force onto a performer kicking a football.
- there is a reaction force between the foot and the ball and the foot and the ground
- as the player kicks the ball, they generate a muscular force (action)
- causes the ball to move and accelerate in the direction the force is applied
- there is an equal and opposite reaction force applied by the ball to the footballers foot and the ground applies an equal and opposite reaction to the other foot
- this allows the player to transfer their weight forwards as they kick the ball
what is friction?
occurs when two or more bodies are in contact with one another
what are the 2 types of frictional forces?
static
sliding
what is the static force?
the force exerted on one surface by another when there is no motion between the two surfaces
- it is dry friction between stationary surfaces
e.g: friction between the surface of a netball court and the sole of a shoe (the player is not moving)
what is the sliding friction?
when dry friction acts between two surfaces that are moving relative to one another
- when the two bodies in contact have a tendency to slip/slide over each other
what direction does friction act in?
friction acts in opposition to motion
- therefore the direction of the arrow to show friction will be in the opposite direction to the slipping (usually in the same direction as the motion)
when may the arrow change?
in sports like skiing when you want to slide
- the friction is in a forward direction
what are the factors that affect friction?
- surface characteristics
- e.g: sprinter that wears spikes -> increases friction between the spikes and track -> maximising acceleration - temperature of the two surfaces
- e.g: curling -> ice is swept to increase the temperature to reduce friction between the stone and ice (so it travels further) - mass of the objects sliding
- larger mass results in a greater friction
what is air resistance?
a force that acts in the opposite direction to the motion of a body travelling through the air
what does air resistance depend on?
- velocity of the moving body
- the faster the performer, the greater the air resistance - cross-sectional area of the moving body
- larger the CS area, greater the air resistance
e.g: cyclists crouching low over the handlebars - shape and surface characteristics of a moving body
- streamlined shape or a smooth surface = less resistance
e.g: half/full body swimsuits and a swimming cap to create a smooth surface
what is air resistance known as in water?
drag
- much greater drag force in water due to its greater density
how do you draw weight acting on a performer in linear motion?
drawn down from the centre of mass to the ground
how do you draw reaction force acting on a performer in linear motion?
starts from where two bodies are in contact with one another
- drawn in the opposite direction to the action
how do you draw friction acting on a performer in linear motion?
starts from where the two bodies are in contact
- it is opposite to the direction of any potential slipping
- drawn in the same direction as motion
how do you draw air resistance acting on a performer in linear motion?
drawn from the centre of mass
- in the opposing direction of the motion of the body
what does the length of the arrow represent?
reflects the magnitude / size of the force
- longer the arrow, bigger the size
what is the net force?
the resultant force acting on a body when all other forces have been considered
what is a balanced force?
when there are 2 or more forces acting on a body that are equal in size but opposite in direction
e.g: when standing, weight and reaction force are equal in size and opposite in direction
- there is a zero net force and therefore no change in state of motion
what is an unbalanced force?
when a force acting in one direction on a body is larger than a force acting in the opposite direction
e.g: when jumping, the performer accelerates upwards as the reaction force is bigger than the weight force
what happens with the net force in terms of friction?
when the friction force is equal in length to air resistance, the net force is zero
- if the friction arrow is longer, the body will accelerate
- if the friction arrow is shorter, the body will decelerate
what is impulse?
the time it takes a force to be applied to an object or body
(link newton’s first law -> a force is required to change a state of motion of a body)
how do you calculate impulse?
impulse (newton seconds) = force x time
how can you link impulse to newton’s second law?
an increase in impulse will result in an increase in the rate of change of momentum -> which causes a large change in velocity
using impulse how can you increase momentum?
- increasing the amount of muscular force that is applied
- decreasing the amount of time in which a force is applied
using impulse how can you decrease momentum?
increasing the time force acts upon them
- performer pushing their feet hard into the ground to increase the contact time of the foot with the ground so they can decelerate quickly
what are force-time graphs?
they represent impulse
what is a footfall?
the action of the foot in contact with the ground
what is a negative impulse?
when the performer is decelerating
what is a positive impulse?
when the performer is accelerating
what does a net impulse of zero mean?
when the positive and negative impulses are equal
- no acceleration or deceleration
- sprinter is running at a constant velocity
define net impulse.
a combination of positive and negative impulses
