3.1 Motion Flashcards
Speed
Speed is defined as the rate of change of distance
Instantaneous speed
is the speed of an object over a very short time interval. It can be determined by analysing the gradient of a distance-time graph at a given time
Displacement
The displacement of an object is the distance it has travelled in a given direction, so it is a vector quantity, with both magnitude and direction. The velocity of an object is defined as the rate of change of displacement
Acceleration
Acceleration is defined as the rate of change of velocity. Acceleration is a vector quantity. An object is accelerating when its speed is increasing, and decelerating when its speed decreases, and it will also accelerate when its direction of travel changes, such as in circular motion
Velocity time graph
The area under the graph is equal to the displacement. Acceleration is the gradient. inital velocity is velocity which it starts at. final velocity is the velocity which it ends at
What is a projectile
A projectile is an object that is thrown at an angle to the horizontal. and therefore moves in both the horizontal and vertical planes. The horizontal and vertical components of the object’s motion are analysed independently.
What is the stopping distance
stopping distance = total distance = thinking distance + braking distance
What is the Thinking distance
Thinking distance is the distance travelled between the moment the hazard is spotted, and the
moment the driver applies the brake
What is the braking distance
The braking distance is the distance travelled from the time the brake is applied to the time the vehicle comes to a complete stop. The braking distance of the car is proportionate to the square of the initial speed of the car. The thinking distance is affected by the initial speed of the car
How is thinking distance calculated
The thinking distance can be calculated by multiplying the initial speed of the car by the reaction time of the driver
How is braking distance calculated
The braking distance of the car is proportionate to the square of the initial speed of the car
Factors affecting thinking distance
such as tiredness, being under the influence of alcohol or drugs, and other distractions
Factors affecting braking distance
road conditions (ice roads, wet), car conditions (heavy load, bald tires and poor brakes)
Define velocity
The velocity of an object is defined as the rate of change of displacement, or speed in a given direction, making velocity a vector.
What does a straight, horizontal line represent on a displacement-time graph?
A stationary object.
What does a line with a constant, non-zero gradient represent on a displacement-time graph?
An object moving with constant velocity.
What does a curved line represent on a displacement-time graph?
Acceleration (if gradient is increasing) or deceleration (if gradient is decreasing).
What does the area under an acceleration-time graph represent?
Velocity.
Describe how the terminal velocity of an object can be determined using light gates.
● Set up the light gates vertically and measure the distanc between them.
● Connect them to a data logger and then release an object from rest above them, measuring the time it takes for the object to travel between the two gates.
● Using the time and the known distance, you can calculate the velocity of the falling object.
Describe how light gates can also be used to investigate conservation of momentum.
● Place two carts on a linear air track (to reduce friction) with repelling magnets so that they do not stick together.
● Attach card to the top of each cart so that they break the beams of the light gates when they pass.
● Keep one cart stationary and push the other towards it, measuring its velocity before the collision.
● Then measure the velocity of both carts after the collision and calculate the momentum before and after.
Define ‘g’.
The acceleration of free fall, ‘g’, is the acceleration of an object in response to the gravitational attraction between the Earth and the object. g = 9.81m s-2
Describe the experiment in which one can determine ‘g’ using an electromagnet.
● An electromagnet holds a steel ball suspended a measured distance above a surface, then start the timer when the electromagnet is deactivated, and stop it when the surface is hit.
● As the ball was initially resting, u = 0.
● The distance and time are known, so we can use a SUVAT equation: s = ut + 1⁄2 at2
● Calculate ‘a’ which, in this case, is ‘g’.
A ball if projected of a castle at 6m s-1. How does its horizontal velocity change from its launch until it hits the ground?
The horizontal velocity remains the same as there is no acceleration in the horizontal direction.
In projectile motion, what is the vertical acceleration?
The vertical acceleration is equal to gravitational field strength (g) downwards.
