Forces In Motion Flashcards
Define distance?
Total length between two points
Define speed?
Total distance travelled per unit of time
Define displacement?
Distance of an object from a fixed point in a specified direction
Define velocity?
The rate of change of displacement of an object
What is acceleration?
The rate of change of velocity of an object
How do we find instantaneous speed on a graph?
Draw a tangent to the curve
Features of a displacement time graph?
Gradient = velocity
Y intercept = initial displacement
Diagonal straight line represent constant velocity
Curved line represents acceleration
Horizontal line represents rest
Features of a velocity time graph
Gradient = acceleration
Y intercept = initial velocity
Straight line represents uniform acceleration
Positive slope = increase in velocity (positive direction)
Negative slope = increase in velocity (negative direction)
Curved line represents non-uniform acceleration
Horizontal line = constant velocity
Area under the graph = displacement
Features of an acceleration time graph?
Gradient is meaningless
Y intercept = initial acceleration
Horizontal line represents constant acceleration
Area under the graph = change in velocity
Describe the motion of a bouncing ball
Acceleration due to gravity is always in the same direction
Positive velocity when travelling in the positive direction
Negative velocity when travelling in the negative direction
Positive direction is upwards
Negative is downwards
Highest point velocity is zero
At the highest point acceleration is negative whilst at lowest point it’s positive
Suvat key terms
Start from rest :
- u= 0
- t= 0
Falling due to gravity means acceleration is 9.81
Doesn’t matter which way is positive or negative as long as the values are consistent
- if downwards is negative, s must be positive and a must be negative.
How are trolleys used to study collisions?
They are composed of:
A light block of wood or plastic
Ball bearing wheels (to reduce friction)
A spring loaded plunger (for collisions)
A flat top surface to allow stacking or additional masses to be added.
How can we study collisions using air track gliders?
Used to investigate conservation of momentum
Reduce friction so energy lost to overcoming friction is minimised and the collision is as elastic as possible
How are ticket times good for analysing motion?
A long tape attached to a moving trolley and threaded through a device that placed a tick upon the tape at regular intervals of time
The ticket timer will produce a certain number of dots per second on the tape which will travel the same speed as the trolley
Distance between the dots and the time can be used to determine the velocity
Distance between the dots increases shows that the acceleration of the trolley is constant
How can we use light gates?
Measure time taken for a trolley to move a set distance
Card is attached to the top of the trolley as this will interrupt the beams on the light gate
The trolley is released from the top of the ramp with one light gate just in front of the release point and the other at the bottom of the ramp
Time taken to travel between light gates t can be used to workout the initial speed u and final speed v
How can Data loggers be used?
Electronic device that records data and stores it for further analysis
It can be set to record at regular time intervals or when triggered by a sensor such as a light gate
Data loggers are often used as a more accurate way of measuring time and eliminating error from the human reflex speed needed to start a stopwatch
How can Video techniques be used?
Good for determining
Acceleration
Projectile motion
Terminal velocity
FPS must be known as it can be used to determine the time taken
Distance must be known, usually from placing a ruler in the shot with the object
What is the stopping distance?
Distance it travels in the time it takes to stop in response to an emergency
Consists of thinking and braking distance
What is thinking distance?
Distance travelled by the vehicle from when the driver sees a problem and the brakes are applied
= initial speed x reaction time
Factors that affect thinking distance?
Initial speed of the vehicle
Intoxication ie alcohol or drugs
Distractions
Tiredness
What is breaking distance?
Distance travelled by the vehicle after the driver has applied the brake
Work done = braking force x braking distance = 1/2mv^2
Factors affecting braking distance?
Initial speed of the vehicle
Mass of the vehicle
Poor road conditions
Car conditions
What is time of flight?
How long the projectile is in the air (vertical component only)
What is maximum height attained?
The height at which the projectile is momentarily at rest (only vertical component)
What is the range?
Horizontal distance travelled by the projectile (horizontal component only)
What is the only force acting on the projectile?
Gravity
Si unit for newton?
Kg ms^-2
One newton is defined as:
Force that will give a mass of 1kg an acceleration of 1ms^-2
What is tension?
The force experience by a cable, rope, or sting when pulled, hung, rotated or supported
Tension always acts away from the mass
What is a normal contact force?
The force arising when an object rests against another object actions at a 90 degree angle to the plane of contact
What is upthrust?
The upward buoyancy force acting on an object when it is in a fluid
Always acts upwards
What is friction?
Force that arises when two surfaces are in contact with eachother
Always opposes motion
Rules of object on slope (parallel/perpendicular)
Parallel forces must be equal
Perpendicular forces must be equal
Factors affecting drag?
The speed of the object
Objects shape and texture
Density of the fluid
Objects cross sectional area
What is a moment?
Turning effect of a force
Equation for moment?
Moment = force x perpendicular distance from the pivot
What is the principle of moments?
For a system to be in equilibrium, the sum of the clockwise moments must be equal to the sum of the anti-clockwise moments
What is a couple?
Pair of equal and opposite coplanar forces that acts to produce rotation only
A couple consists of?
Pair of forces that are equal in magnitude, opposite in direction, perpendicular to the distance between them
