(5) Forces and Motion Flashcards
Define distance:
Distance is how far an object moves, it doesn’t involve direction (scalar quantity)
Define displacement:
Displacement includes both the distance an object moves (measured in a straight line from start to finish) and the direction. (Vector quantity)
What are the typical values for the speeds of: sound, human walking, running and cycling
Sound = 330 m/s
Human walking = 1.5 m/s
Human running = 3 m/s
Cycling = 6 m/s
What factors does the speed of walking, running or cycling depend on?
- age
- terrain
- fitness
- distance travelled
What is the equation linking distance speed and time?
Distance = speed x time
Why can an object travelling at a constant speed in a circle not have a constant velocity?
- speed is a scalar quantity
- velocity is a vector meaning is can only be constant if the direction is constant and in a circular motion the direction is continuously changing
How can speed be calculated from a distance time graph?
Speed is equal to the gradient of the graph
How do you calculate speed from a distance time graph for an accelerating object?
Draw a tangent to the curve at the required time and calculate the gradient
What is the equation for acceleration?
Acceleration = change is velocity / time taken
How can the distance travelled by an object be calculated from a velocity time graph?
Equal to the area under the graph
What is the equation for velocity?
(Final velocity)² - (initial velocity)² = 2 x acceleration x distance
[ v² - u² = 2 x a x s ]
What is an approximate value for the acceleration of an object in free fall under the earths surface?
9.8 m/s
What can be said about the resultant force acting on an object when it is falling at terminal velocity?
It’s is zero
- when at terminal velocity the object is moving at a constant speed and so isn’t accelerating
State Newton’s first law for stationary objects:
If the resultant force on a stationary object is zero, the object will remain at rest
State Newton first law for a moving object?
If the resultant force on a moving object is zero, the object will remain at a constant velocity (same speed in the same direction)
What happens to the resultant force is an object is going at a constant speed?
If an object is at a constant speed, the resultant forces is balanced with driving force and the velocity of an object only changes if a resultant force is acting on it.
What is inertia?
The tendency to resist any change in motion, staying at rest or uniform motion
What is Newton’s second law?
The acceleration of an object is proportional to the resultant force acting on the object and inversely proportional to the mass of an object
State the equation for Newton’s second law?
Resultant force = mass x acceleration
What is inertial mass?
A measure of how difficult it is to change the velocity of an object. It is defined as the ratio of force over acceleration
REQUIRED PRACTICAL 6: effect of force on acceleration on an object if constant mass
Measuring how long it takes for a trolly to move distance with diff et forces applied to it. Set up on a bench pulley with a meter ruler, string and weight stack.
What is Newton’s third law?
Whenever two objects interact, the forces they exert on each other are equal and opposite. (Can be used in equilibrium situations)
What is the stopping distance of a vehicle equal to?
Equal to the sum of the distance the vehicle travels during the driver reaction time (thinking distance) and the distance it travels under the braking force.
For a given braking distance, if the vehicles speed is increased what happens to the braking distance?
The greater the speed of the vehicle the greater the stopping distance
What are the typical reaction times of humans?
0.2s - 0.9s
What factors affect the drivers reaction time?
• tiredness
• drugs
• alcohol
What factors affect braking distance?
• Icy roads
• Wind
• Poor vehicle condition
Describe the energy transfers that take place when a car applies it brakes:
Work done by the friction force between the brakes and the wheel reduces the kinetic energy of the vehicle (increasing the temperature of the brakes)
Does a greater braking force cause larger or smaller deceleration?
Larger deceleration
These may cause brakes to overheat and the driver may also lose control of the vehicle.
