On the Move Flashcards
Name the 5 SUVAT equations
s = [ (u+v)/2 ]t v = u + at s = ut + ½at² s = vt - ½at² v² = u² + 2as
Explain why a projectile will only experience an acceleration in the vertical direction
Vertical and horizontal motion are completely independent
The force of gravity only acts vertically on an object
Define displacement
The distance in a given direction
Define speed
The change of distance per unit time
Define velocity
The change of displacement per unit time
speed in a given direction
Give the shape of the line for a graph of distance vs. time for an object at constant speed
A straight line (linear)
Describe how the speed of an object can be calculated for a graph of distance against time where the line is:
i) linear
ii) non-linear
i) speed = gradient
ii) speed at a time = gradient of curve at that time, which can be measured by drawing a tangent to the curve and measuring the gradient of the tangent
Define acceleration
The change in velocity per unit time`
Give the equation for uniform acceleration, given the object’s initial and final velocity
a = (v - u) / t
What does the gradient of the line represent for a velocity vs. time graph?
The acceleration
What does the area under the line represent for a velocity vs. time graph?
The displacement
Describe a method to investigate the acceleration due to gravity of an object in free fall
Setting up a stroboscope at a known flash rate and a camera and dropping a ball in front of a metre rule and a dark background. The metre rule acts as a scale, so the displacement of the ball between each image (when the stroboscope flashes) can be measured
Describe the difference between a displacement vs. time graph and a distance vs. time graph for a ball thrown vertically upwards
Since displacement is distance in a given direction, a ball thrown into the air will finish with 0 displacement, but a distance of twice the maximum height.
Therefore overtime, the displacement will increase, hit a maximum and decrease, whereas the distance will increase to the maximum height (where it levels off) and then increase yet again
Define a projectile
A projectile is any object acted upon by the force of gravity
What 3 key principles apply to all projectiles?
1) The acceleration of the object is always equal to g and is always downwards
2) The horizontal velocity of the object is constant because the acceleration of the object doesn’t have a horizontal component
3) The motion in the horizontal and vertical directions are independent of each other
For an object projected horizontally, give 3 statements that will always be true
1) Its path through the air becomes steeper as it drops
2) The faster it is projected, the further away it will land
3) The time taken for it to land doesn’t depend on how fast it is projected
Describe an experiment to investigate horizontal projection and explain its results
- Setting up a stroboscope and camera with a slow shutter. Drop one ball at the same time as a second ball being given horizontal projection.
- The horizontal position of the 2nd ball changes by equal distances between successive flashes because the horizontal component of the ball’s velocity is constant
- The vertical position of the 1st and 2nd ball changes at the same rate, because they both have the same vertical component of velocity at any instant
Give an equation for the horizontal component of an object projected horizontally
Displacement x = ut
Give an equation for the vertical component of an object projected horizontally
Displacement y = ½gt²
Give the conditions required for the motion of an object to be described as projectile-like motion
Any form of motion where an object experiences a constant acceleration in a different direction to its velocity
Give 2 examples of objects moving with projectile-like motion and explain why
1) The path of a ball rolling across an inclined board will be a projectile path. Its path is parabolic because the object is subjected to constant acceleration down the board but its initial velocity is across the board
2) The path of a beam of electrons directed between two oppositely charged plates will be parabolic because each electron is acted on by a constant force towards the positive plate (due to charge) but its motion parallel to the plates is at 0 acceleration
Describe a mathematical method to find the speed of an object with horizontal projection when given the components of its velocity in the horizontal and vertical direction
Treat the velocities as sides of a triangle, and solve to find the hypotenuse
e.g. if the velocity of the horizontal component = vₓ
and the velocity of the vertical component = vᵧ
Then the speed at time t is given by
√(vₓ² + vᵧ²)
For an object in 0g, projected into the air at speed U in the direction at angle θ, give the horizontal and vertical components for its displacement at time t
Horizontal component x = Ut cosθ
Vertical component y = Ut sinθ
How much higher would an object projected in 0g be than when acted upon by gravity if its initial speed was U in the direction at angle θ?
It would be ½gt² higher
