Forces Flashcards
What do objects do in terms of forces?
Exert equal and opposite forces on each other-sometimes known as action reaction forces
If a car hits a barrier what does the barrier exert on the car in terms of force?
The barrier exerts a force on the car that is equal in size and in the opposite direction
In what direction does weight always act?
Downward
What is the resultant force?
Is the single force that would have the same effect on the object as all the original forces acting together
What does could it mean if the resultant force on an object is zero?
If the object is at rest, it will stay at rest
If the object is moving, it will carry on moving at the same speed in the same direction
If an object is accelerating what 3 things could it be doing?
Speeding up
Slowing down
Changing direction
When the resultant force of an object is not zero, what will happen to the object?
It will accelerate in the direction of the force
What could happen if the resultant force is not at zero?
If the object is at rest, it will accelerate in the direction of of the resultant force
If the object is moving in the same direction as the resultant force, it will accelerate in that direction
If the object is moving in the opposite direction to the resultant force it will decelerate
What is the unit of resultant force?
Newtons
What is the resultant force of a 4n force and a 3n force acting in the same direction?
7n in the same direction as the two forces
What doe s a resultant force always cause?
An acceleration, if there is no acceleration the resultant force must be zero
What equation is used to calculate the resultant force?
F=MxA
What is mass measured in?
Kg
What is weight measured in?
Newtons
The greater the resultant force, what does that mean about the acceleration?
The acceleration is greater
If the mass of an object is large, what does that mean about the size of the force needed?
The bigger the mass, the bigger the force needed to give it a particular acceleration
What is the resultant force on a car travelling at a steady speed on a straight horizontal road?
Zero as a steady speed mean no acceleration so no resultant force
What happens to the acceleration of an object as the resultant force on it decreases?
Acceleration decreases
The faster the speed of a vehicle…
Braking distance
The bigger the deceleration need to stop it therefore a bigger braking distance needed
What is the stopping distance?
The distance a vehicle travels during the drivers thinking distance plus the distance travels under the braking distance
What is the thinking distance?
The distance travelled by the vehicle in the time it takes the driver to react
What is the braking distance?
The distance travelled by a vehicle during the time it’s brakes act
What can affect the thinking distance?
Alcohol
Drugs
What can affect braking distance?
Poorly maintained roads
The condition of the car eg worn tyres or worn breaks will increase braking distance
Weather conditions
What is the relationship between stopping distance, thinking distance and braking distance?
Stopping distance= thinking + braking distance
What is the weight of an object?
The force of gravity on the object
What is mass?
The quantity of matter in it
An object acted on by only gravity accelerates by how much?
10m/s
If an object falls freely what is the resultant force acting on it?
The force of gravity
When an object falls through a liquid what force does the liquid exert on the object and what effect does it have?
A drag force which restricts its motion
Why does an object dropped in a fluid initially accelerate?
There is a resultant force acting on it
What eventually halogens to an object falling in a fluid?
It reaches a terminal velocity as the resultant force becomes zero
What are forces measured in?
Newtons
What is the extension of a spring?
The increase in length from the original
What does elastic mean?
A material is elastic if it is able to regain its shape after it has been squashed or stretched
If you plot a graph of extension against force applied for a spring what sort of line will we Obtain?
A line that is directly proportional which passes through the origin
What is limit of proportionality?
The limit for hooked law applied to the extension of a stretched Spring
What does hooked law state?
The extension is directly proportional to the force applied provided the limit of proportionality is not exceeded
If a spring is stiff what does that mean about its spring constant?
The stiffer the spring, the greater the spring constant
What is spring constant measured in?
N/M
What happens when an elastic object is stretched?
Work is done this is stored as elastic potential energy
What happens when the stretching force of a string is removed?
The stored energy is released
How can we tell when a spring has exceeded its limit of proportionality?
The graph of extension force against is no longer a straight line
What is fuel economy?
If you reduce the speed of a vehicle it reduces the amount if fuel it uses to travel a particular distance
What Improves fuel Economy?
Reducing air resistance makes a vehicle more streamlined (fitting a wind deflector)
What are average speed cameras?
Cameras that are linked in pair that calculate the average speed of a vehicle to catch out drivers who slow down then speed up for cameras
What do anti skid surfaces do?
They refuse or prevent skidding. They are rougher than normal road surfaces, increasing the friction between the tyres and the road. They are used
What can a force do?
Change the shape of an object or change its state of rest or motion
What force makes a car move?
Engine force or motive force
If the resultant force is zero what could that mean about the forces acting on it?
They are balanced
What is the total resultant force if the forces are in the same direction?
Their sum is the resultant force
What is the total resultant force if the forces are in the opposite direction?
The difference in the force subtract
Why will a falling object accelerate at first?
The weight is greater than the drag force
As the object falls faster what will happen?
The drag forces increase so the acceleration will decrease
What happens when the 2 forces on a falling object balance?
The acceleration is zero and the terminal velocity is reached
Describe the drag force on a parachutist
At first the drag force is due to the parachutist alone
Later on the drag force is due to the parachute
Why do rubber bands and polythene strips not obey Hookes law?
They have a low limit of proportionality and so do not produce a straight line graph
The force of the friction of the ground on the tyre is in the ….
Forward direction
The force of the tyre on the ground is in the ….
Reverse direction
The velocity …. If the resultant force is in the ….. Direction to the velocity
Decrease
Opposite
The velocity increases If the resultant force is in the ….. Direction to the velocity
Same
The …. The mass of an object the …. It’s acceleration for a given …
Greater
Smaller
Force
What is the thinking distance equal to?
The cars speed multiplied by the drivers reaction time. It is proportional to the cars speed
What is the breaking distance equal to?
The average speed of the car during the braking multiplied by the breaking time. The breaking distance is proportional to the square of the cars speed
What is gravitational field strength usually on earth?
10n/kg
Drag force increased with …
Speed
The acceleration of an object decrease as it falls because …
The drag forces increases as it speeds up
What is terminal velocity?
When the resultant force becomes zero so no longer accelerates
