Forces (5) - Pt3 Flashcards
What’s the speed of a:
- car
- train
- plane
- car: 25m/s
- train: 55m/s
- plane 259m/s
What’s the speed of sound. And what can effect its speed?
330m/s in air
It can change depending on what the sound waves are travel traveling through
What effects the speed of a person?
- fitness and age
- terrain they’re on
What can effect the speed of wind?
- temperature
- atmospheric pressure
- large structures (eg. Forests reduce the speed of the air traveling through them)
What’s acceleration?
The change in velocity in a certain amount of time
How would you calculate the average acceleration of an object?
Acceleration (m/s*2) = change in velocity (m/s) / time (s)
a= change in v/ t
What’s deceleration?
Negative acceleration (the change in velocity is negative)
What’s uniform acceleration?
Constant acceleration
What’s the equation the links velocity, acceleration and distance?
Final velocity (m/s)*2 - initial velocity (m/s)*2 = 2 x acceleration (m/s*2) x distance (m) V*2-u*2 = 2as
What does the gradient of a distance-time graph mean?
Speed
The steeper the graph the faster it’s going
What does a flat section on a distance-time graph mean?
Where it’s stationary
What do the straight uphill section on a distance-time graph mean?
It’s traveling at a steady speed
What does a curve on a distance-time graph mean?
Acceleration (a steeping curve means it’s speeding up) or deceleration (a levelling of curve means it’s slowing down)
(Draw a tangent to a point of the curve if you want to find the speed)
What does the gradient of a velocity-time graph mean?
The gradient=acceleration
What does a flat section on a velocity-time graph mean?
Represent traveling at a steady speed
What does the steepness of a velocity-time graph mean?
- the steeper the graph the greater the acceleration or deceleration
- uphill sections are constant acceleration
- downhill sections are constant deceleration
What does a curve on a velocity-time graph mean?
Changing acceleration
What does the area under a a velocity-time graph mean?
The distance travelled
If an object has no force propelling it along what will happen?
- It will always slow down and stop because of friction
- Friction always acts in the opposite direction to movement
- To be at a steady speed the driving force need to equal the fictional forces
When do you get friction?
- between 2 surfaces in contact
- when an object passes through a fluid (drag)
What’s drag? And give an example of a type of drag?
- it’s the resistance you get in a fluid (a gas or liquid)
- eg. Air resistance
- drag increase as speed increses
How can you reduce drag?
- By keeping the shape streamlined
- this allows the fluid to flow easily across it
Explain how object’s falling through fluids reach a terminal?
- at the start the force of gravity is a lot more than the frictional Force, so it accelerates
- as the speed increases friction builds up reducing the acceleration
- until the frictional forces are equal to the accelerating force (so the resultant force is 0)
- it will have reached terminal velocity and will fall at a steady speed
What 2 things affect terminal velocity?
Shape and area
Using the example of a skydiver explain how the frictional force depends on the shape and area?
- without the parachute open he has a small area. He reaches a very fast terminal velocity
- but with the parachute open there’s a lot more area resistance. So he has a lot slower terminal velocity
What’s Newton’s first law of motion?
- If the resultant force on a stationary object is 0, the object will remain stationary.
- If the resultant force on a moving object is 0, it’ll just carry on moving at the same velocity
If the resultant force isn’t 0 what happens?
Acceleration (or deceleration) in the direction of the force
What different ways could they refer to “acceleration” (or deceleration) as?
- Starting
- Stopping
- Speeding up
- Slowing down
- Changing directions
- (On a free body diagram the arrows will be unequal)
What’s the relationship between resultant force and acceleration?
They’re directly proportional
What’s the relationship Between acceleration and mass (for a fixed resultant force)?
Acceleration is inversely proportional to mass
