Forces Flashcards
Force
A force can change the motion of an object (N)
Newton
The unit of force (N)
Resultant force
The single force that has the same effect as all the objects acting on an object
Mass
The quantity of matter in an object - a measure of the difficulty of changing the motion of an object (kg)
Stopping distance
Thinking distance + braking distance (m)
Thinking distance
The distance travelled by the vehicle in the time it takes the driver to react
Braking distance
The distance travelled by the vehicle during the time its brakes act
Weight
The force of gravity on an object (N)
Gravitational field strength (g)
The force of gravity on an object of mass 1 kg (N/kg)
Drag force
A force opposing the motion of an object due to a fluid flowing past the object as it moves
Terminal velocity
The velocity an object falling in a fluid reaches when the weight is equal to the drag force on it
f=ma
force (N) = mass (kg) x acceleration (m/s^2)
w=mg
weight (N) = mass (kg) x acceleration due to gravity (m/s^2)
Elastic
A material able to regain its shape after being squashed or stretched
Directly proportional
Shown by a graph if the line of best fit is a straight line through the origin
Limit of proportionality
The limit for Hooke’s law applied to the extension of a stretched spring
Hooke’s law
The extension of a spring is directly proportional to the force applied, provided its limit of proportionality is not exceeded
f=ke
force (N) = spring constant of a spring (N/m) x extension of a spring (m)
What can forces do?
A force can change the shape of an object or change its motion or state of rest
What is the SI unit of force?
Newton (N)
When two objects interact, what can we say about the forces acting?
The forces are always equal and opposite to each other
What happens when the resultant force on an object is zero?
The object stays at rest or at constant velocity
What happens when the resultant force on an object is not zero?
The velocity of the object will change
How do we calculate the resultant force when an object is acted on by two forces acting along the same line?
The force is the their sum if the objects are acting in the same direction, and the difference if the forces act in opposite directions
How does the acceleration of an object depend on the size of the resultant force?
The bigger the resultant force, the greater the acceleration
What effect does the mass of the object have on its acceleration?
The greater the mass of the object, the smaller its acceleration for a given force
What forces oppose the driving force of a car?
Friction and air resistance
What does the stopping distance of a vehicle depend on?
The thinking distance and braking distance
What factors can increase the thinking distance?
Tiredness, alcohol and drugs affect reaction times, and the faster the vehicle is traveling, the greater the thinking distance
What factors can affect the braking distance?
The faster the vehicle is traveling, the further it must travel before it stops. Adverse road conditions (on wet or icy roads drivers have to brake with less force to avoid skidding) or a poorly maintained car increase the braking distance
What is the difference between mass and weight
The weight of an object is the force of gravity on it, whereas its mass is the quantity of matter in it
What can we say about the motion of a falling object acted on only by gravity?
It will accelerate at 9.8 m/s² (round to 10)
How do we measure the extension of an object when it is stretched?
The extension is the difference between the length of the spring and the original length
How does the extension of a spring vary with the force applied to it?
The extension of a spring is directly proportional to the force applied to it, provided the limit of proportionality is not exceeded
What is the spring constant of a spring?
The spring constant of a spring is the force per unit extension needed to stretch it
How can the fuel economy of road vehicles be improved?
Reducing the speed or fitting a wind deflector
What is an average speed camera?
Average speed cameras are linked in pairs and the measure the average speed of a vehicle
What is the point of anti-skid road surfaces?
They increase the friction between a car tyre and the road surface, thus reducing or even preventing altogether skids
