Projectile motion Flashcards
What is a projectile
A projectile is a body that is moving within a fluid, not in contact with the ground.
Fluids include air and water
Three release factors affect the horizontal distance that a projectile will travel before landing
Height of release
Speed of release
Angle of release
What is height of release and what is its effect on projectiles
- Height of release: the level (height) from which a projectile is released (let go of) compared to the level (height) of the landing surface.
The higher the release height from the landing height, the further the horizontal distance travelled. Eg: raised tee height (above fairway) in golf leads to the ball travelling further before landing
What is speed of release and what is its effect on projectiles
- Speed of release: how fast a body is travelling at the moment it
becomes a projectile.
The greater the speed of release, the further the horizontal distance
travelled. Eg A fast arm in javelin throwing leads to greater distance.
What is angle of release and what is its effect on projectiles
- Angle of release: the projection angle of the object, measured between the horizontal and the direction of the projectile at release.
The optimal angle of release is 45 degrees if the height of release is the same as landing. Eg: Long jump
If the landing height is lower than release: Eg Shot Put, then optimal release angle less than 45 degrees
Paralelogram of forces
This method uses a parallelogram (a four sided shape where opposite sides are parallel to each other) to show the size and direction of the resultant force acting on a body.
Start with two force arrows with a common origin.
A parallelogram is drawn where opposite sides of the shape are parallel to the force arrows, and drawn with a dotted line.
The resultant force arrow is drawn diagonally across the parallelogram from the origin of the two forces.
The resultant force (R) shows the direction and size of the resultant force.
This information can be used to determine the acceleration of the
body by applying Newton’s second law : f=ma
2 patterns of flight
Parabola/parabolic: A uniform curve that is symmetrical about its highest point.
Non-parabolic: A curve that is not symmetrical (asymmetric) about its highest point
The shape of the flight path of a body or object depends on the relative sizes of the two forces acting: weight and air resistance
Parabolic flight path
If weight is the only force acting on a body, then its flight path is parabolic.
So if weight is the dominant force acting on a body (because the body has a large mass) and it has very little air resistance, then the flight path shape is very close to being parabolic or symmetrical. Eg: Shot put
A parallelogram diagram shows the resultant force is large and that its direction is close to vertical.
The high mass means that air resistance has little effect on the velocity of the body during flight.
The size and direction of the resultant force on the shot changes very little during each phase of flight = symmetrical, parabolic flight path.
Non-parabolic flight path
If weight is small, and air resistance is large then the flight path shape is non-parabolic or asymmetric. Eg: Badminton shuttle
This is because the force of air resistance is able to overcome the inertia (small mass) of the body, and decrease its velocity.
Decreasing velocity causes decreasing air resistance.
As the flight continues the body becomes increasingly under the influence of its weight, rather than air resistance.
The parallelogram of forces shows that the size of the resultant force decreases, and the direction it acts in becomes further from the direction of AR. (Increasing angle between AR and R)
This gives a non- parabolic flight shape
What is an aerofoil and angle of attack
Aerofoil: A streamlined structure with at least one curved surface. Aerofoils can be symmetrical Eg: A javelin or discus, or asymmetrical Eg: A ski jumper or F1 racing car spoiler
Angle of attack: the angle at which a projectile is tilted or presented to the air
What is Bernoulli’s principle
The faster fluids flow, the less pressure they exert. The slower fluids flow, the more pressure they exert. This can create a lift force on a projectile
Bernoulli’s principle applied to aerofoils
When an aerofoil is projected with an angle of attack, the air flows differently over the top surface than over the bottom surface: this can create a lift force.
Above projectile: Air travels further and faster, This creates low pressure.
Below projectile: Air travels less far and slower, This creates high pressure.
The pressure differential causes an upwards lift force from high to low pressure
Upwards lift force
The upwards lift force reduces the impact of weight.
The resultant force has a smaller downwards component.
Flight time is extended and therefore the horizontal distance travelled increases.
The flight path is made non-parabolic
Bernoulli’s principle applied to reverse aerofoils
Reverse aerofoil: An aerofoil positioned with its curved surface facing downwards and its flatter surface facing upwards, causes downforce
Downforce: A force pushing downward on a body
A reverse aerofoil also causes a difference in the air flow above + below it: the Bernoulli principle is the same, but the high and low pressures are on opposite sides of the aerofoil
Above the reverse aerofoil: slow flow, high pressure
Below the reverse aerofoil: fast flow, low pressure
The wing on the back of the F1 car is a reverse aerofoil. Downforce acts on it causing increased friction and grip between the tyres + track
