Forces and Movement Flashcards
What is the equation for Newtons 2nd Law? (force)
Force = Mass*Acceleration or F = m*a
What do forces do to objects?
Forces make objects:
- speed up/slow down
- change direction
- start or stop
- change shape
What is the relationship (equation) between weight, mass and g?
Weight = mass*g
What is the gravitational field strength measured in?
N/kg
When would your weight change?
Weight = mass*g and since mass is constant, g would have to change for your weight to change. G is 1.7 on the moon so if you went to the moon your weight would change.
What main forces will act on you if you fall through a fluid.
Gravitational force (downwards) and frictional force (upwards), ignoring Archimedean force.
How is the size of the resistive force relative to the speed on a falling object?
The size the resistive force is approximately on the speed squared. The resistive force is the drag force.
What will initially happen as a skydiver jumps out of a plane?
There will be zero resistive force and she will be accelerating downwards a rate of 10m/s/s.
What will happen when a skydiver picks up speed?
The drag force grows, reducing the overall force downwards and thus reducing the acceleration.
What will eventually happen to a free falling skydiver?
The resistive force will become equal to the weight making the overall force and acceleration zero so the object will now fall at a constant velocity.
What is it called when an object is falling at a constant velocity?
Terminal velocity.
What happens when a skydiver at terminal velocity opens their parachute?
The resistive force is larger than the weight of the skydiver so he is decelerating (but still falling downwards) until his speed falls to a point where his weight again balances the drag force. He will reach terminal velocity again.
What actually makes a car decelerate when you apply the brakes?
The friction force between the tires and the road. This force should be as large as possible to make the deceleration as big as possible.
Why is over-breaking bad and what factors affect it?
Overbreaking makes it more likely the car will skid and when this happens there is less friction between the wheels of the car and the road. Poor tires, water, ice or oil on the road surface will make the maximum braking force you can apply without skidding much lower so your deceleration is lower.
What is the overall stopping distance?
A sum of the thinking and breaking distance.
What is the thinking distance?
The distance you travel while thinking about putting your foot on the break.
What is the breaking distance?
The distance the car travels once the breaks have been applied.
How is the thinking distance related to the speed you are driving at?
It is proportional to the speed.
How is the breaking distance related to the speed you are driving at?
On the speed SQUARED.
How do you calculate breaking distance?
Breaking distance = Average speed*time
What factors while affect your reaction time?
Age, eyesight, tiredness, drugs, alcohol, medicines, mobile phones etc.
What factors will affect the breaking distance?
- The speed
- The mass of the car
- The braking force
or even anything on the road such as ice that reduces the friction
What is the law to do with acceleration due to gravity and weight?
All object accelerate at the same soeed on earth, provided that the effect of air resistance can be ignored. This can be demonstrated by the ‘coin and feather’ eperiment in which the two objects take exactly the same amount of time to fall through a tube with no air in it.
Why does a light object (e.g. a feather) fall slower than a heavy object (e.g. a hammer), even though it has a lower force of air resistance?
Because the feather has a lower mass so it reaches terminal velocity (when drag=weight) sooner than the hammer
This is becasue a smaller drag force is needed to the avergae velocity of the feather is lower so it falls slower
