Forces Flashcards
What can forces do?
A force can change the shape of an object or change its state of res or its motion.
What is the unit of force?
Newton (N)
When two objects interact, what can we say about the forces acting?
When two objects interact, they always exert equal and opposite forces on each other.
What force makes a car move?
Driving force.
Sometimes called engine force / motive force
What is driving force due to?
It is due to friction between the ground and tyre of each drive wheel.
When does friction act when there is a driving force on the car
Friction acts where the tyre is in contact with the ground.
What is a resultant force?
A single force that has the same effect as all the forces acting on an object.
What happens if the resultant for on an object is zero?
The object remains stationary or moves at constant velocity.
What happens if the resultant for 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 resultant force is:
•their sum if the forces act in the same direction.
•their difference if the forces act in opposite directions.
What is the equation for the resultant force?
Resultant force = mass x acceleration
How does acceleration if an object depend on the size of the resultant force?
The bigger the resultant force on an object, the greater its acceleration is.
What effect does the mass of the object have on its acceleration?
The greater the mass of an object is, the smaller its acceleration is for a given force.
What happens to the velocity if the resultant force is in the same direction as the velocity?
The velocity increases.
What happens to the velocity if the resultant force is in the opposite direction to its velocity?
The velocity decreases (decelerates).
What happens to the acceleration if it’s in the same direction as its velocity?
The acceleration is positive.
What happens to the acceleration if it’s in the opposite direction to its velocity?
The acceleration is negative.
What forces oppose the driving force of a car?
Friction and air resistance.
What does the stopping distance if a vehicle depend on?
Thinking distance and braking distance
What is thinking distance?
The distance travelled by the vehicle during the driver’s reaction time.
What is braking distance?
The distance travelled by the vehicle during the time the braking force acts.
What does braking force depend on?
- the speed of a vehicle when the brakes are first applied.
* the mass of the vehicle.
What factors can increase the stopping distance of a vehicle?
- tiredness, alcohol and drugs.
- distractions (mobile phone).
- high speed.
- adverse road conditions.
- poor weather conditions.
- poorly maintained vehicles.
What is mass?
The quantity of matter in an object.
What is mass measured in?
Kilograms (kg)
What is weight?
The force of gravity on an object.
What is weight measured in?
Newtons (N)
What is the weight of an object with a mass of 1kg?
10N
What can we say about the motion of a falling object acted on only by gravity?
It accelerated at about 10 m/s2.
What is the gravitational field strength at Earth’s surface?
10N/kg
What is the equation of weight?
Weight (N) = mass (kg) x gravitational field strength (N/kg)
What is drag force?
A force opposing the motion of an object due to fluid flowing past the object as it moves.
What is terminal velocity?
The velocity reached by an object when the drag force on it is equal and opposite to the force making it move.
What is the drag force called when the object moves through air?
Air resistance.
How do we know if an object is elastic?
An elastic object regains its original shape when the forces deforming it are removed.
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 its original length.
What is Hooke’s law?
The extension of a spring is directly proportional to the force applied, provided its limit of proportionality is not exceeded.
What is the equation of Hooke’s law?
Force applied (N) = spring constant (N/m) x extension (m)
What is the spring constant of a spring?
The force per unit extension needed to extend the spring, assuming its limit of proportionality is not reached.
How does the stiffness of a spring affect the spring constant?
The stiffer a spring is, the greater its spring constant is.
How can the fuel economy of road vehicles be improved?
- reducing the speed
* fitting a wind deflator
What is an average speed camera?
Average speed cameras are linked in pairs and they measure the average speed of a vehicle.
How do anti-skid surfaces reduce skids?
They increase the friction between a car tyre and the road surface.
