P3 - Speed, Distance & Acceleration, Mass, Weight, & Gravity, Forces, Friction Forces, Terminal Speed Flashcards
How do you find the speed of an object?
You need to measure the distance it travels and the time it takes, then the speed is calculated in meters per second.
For an object, what does a greater speed mean?
The greater the speed of an object, the further the distance it can travel in a certain time, or the shorter the time it takes to go a certain distance.
What does the gradient on a distance time graph tell you?
The gradient tells you the speed.
What does a flat section on a distance-time graph represent?
The flat section on a distance-time graph represents where the object.
What does a steeper gradient represent?
Distance - Time Graphs
The steeper the gradient the greater the speed.
What do curved sections on a distance-time graph represent?
They represent acceleration or deceleration.
What does a steepening curve represent?(Distance Time Graph )
A steepening curve means it is speeding up ( accelerating )
What does a levelling off curve represent?(Distance Time Graph )
A levelling off curve means it is slowing down.
What is acceleration?
Acceleration is how quickly speed is changing.
What is deceleration?
( A negative Acceleration )
A decrease in speed.
On a speed-time graph what does gradient represent?
The gradient represents acceleration.
On a speed-time graph what do the flat sections represent?
The flat sections represent steady speed.
What does a steeper gradient mean for the acceleration on a speed-time graph?
The steeper the gradient, the greater the acceleration or deceleration.
What does a curve mean for an speed-time graph?
A curve means a non uniform ( changing ) acceleration or deceleration.
How can you find the distance travelled on a speed time graph?
The distance travelled in any time interval is equal to the area under the graph.
What is the speed of an object?
The speed of an object is just how fast it is going, there are no directions involved.
What is velocity?
Velocity is a vector, it describes both the speed and direction of an object.
What does Gravity do at the surface of a planet?
On the surface of a planet, gravity makes all things accelerate towards the ground, all with the same acceleration, g.
what is “g” ( gravitational field strength)?
G is the acceleration due to gravity and is also known as the gravitational field strength.
What is the value of “g” on Earth?
The value of “g” on earth is 10 m/s(squared) or 10 N/Kg).
It is different on other planets, and can vary in different places on Earth.
g will be slightly different down a mineshaft compared to the top of a mountain.
It is not affected by changes in the atmosphere.
Gravity gives an object its…
Gravity gives an object its weight.
What is weight caused by?
Weight is caused by the pull of gravity.
What is mass?
Mass is the amount of matter ( or “stuff” ) an object contains. For any given object this will have the same value anywhere in the universe.
What is weight measured in?
Weight is a force measured in newtons
What is mass measured in?
Mass is not a force, it is measured in kilograms.
Why do objects have different weights on the moon and the Earth?
The gravitational pull of the Moon is weaker than the gravitational pull of the Earth.
What is a force?
A force is a simply a push or a pull, there are six different types of force.
What are the six different types of force?
- Gravity or Weight, always acting straight downwards
- Reaction force from a surface, usually acting straight upwards
- Thrust or push or pull due to an engine or rocket, speeding something up
- Drag or Air resistance or Friction, which is slowing something down
- Lift due to an aeroplane wing
- Tension in a rope or cable.
How must the forces be balanced for an object to be stationary?
- The force of gravity ( or weight ) is acting downwards.
- This causes a reaction force from the surface pushing up the object
- This is the only way it can be in balance, the force arrows the same size
In a stationary object, why does it need a reaction force?
Without a reaction force it would accelerate downwards due to the pull of gravity.
In a stationary object, why must the horizontal forces be equal?
They must equal and opposite, because otherwise the object would accelerate sideways.
What is the size of forces in an object travelling at steady horizontal/vertical speed?
All of the forces are balanced.
In an object travelling at steady speed, why must all of the forces be equal?
The forces must stay in balance because otherwise you would get acceleration/deceleration, not steady speed.
In an object with horizontal/vertical acceleration, why must the force be unbalanced?
- You only get acceleration with an overall resultant ( unbalanced ) force.
- The bigger the unbalanced force, the greater the acceleration
- On a force diagram the arrows will be unequal.
What direction does friction act?
When an object is moving ( or trying to move ) friction acts in the direction that opposes movement.
What does the force of friction try to do?
The force of friction will match the size of the force trying to move it, up to a point, after this the friction will be less than the other force and the object will move.
What is the purpose of friction?
Friction will act to make the moving object slow down and stop.
Why do objects need a driving force?
To travel at steady speed, objects always need a driving force to overcome the friction.
What are the three main ways in which friction occurs?
- Friction between solid surfaces which are gripping.
- Friction between solid surfaces which are sliding past each other
- Resistance or “drag” from fluids ( liquids or gases, e.g. air).
What can increase drag?
The larger the area of the object, the greater the drag.
How can objects be changed to reduce drag?
To reduce drag, the area and shape are streamlined and reduced, like wedge shaped sports cars.
What design features of cars increase drag?
- Roof boxes on cars spoil the streamlined shape, and they slow down the car.
Windows can also increase drag, if they are open.
How are parachutes designed to slow you down?
Parachutes often have large area to give a high drag to slow you down, for a given thrust the higher the drag, the lower the top speed.
In a fluid, how does drag work?
In a fluid, friction (drag) always increases as the speed increases.
How do objects reach terminal speed?
- When objects first set off, they have much more force accelerating them than resistance slowing them down.
- As the speed increases the resistance increases as well.
- This gradually reduces the acceleration until the resistance force ( friction or drag ) is equal to the accelerating force ( weight or thrust ) so it can’t accelerate any more. the forces are balanced.
- It will have reached its maximum speed or terminal speed.
What does the terminal speed of any moving object depend on?
The terminal speed of any moving object depends on its drag compared to its driving force, ( weight for a falling object, thrust for, e.g. a car ).
What effect does drag have on terminal speed?
The greater the drag, the lower the terminal speed of the object.
What does drag depend on?
Drag depends on the shape and area.
