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Flashcards in Forces 2 Deck (11):

What is acceleration and how do we measure it?

Acceleration is how quickly velocity changes
It can be a change in speed or direction or both
Acceleration = change in velocity/ time taken
Final velocity - initial velocity divided by acceleration x time or
(V-u)/a x t
Acceleration is measured in m/s2


Explain velocity time graphs

Gradient = acceleration
Flat = constant steady speed
Steeper the graph = greater the acceleration or deceleration
Gradient Uphill = acceleration
Gradient Downhill = deceleration
Curve = changing acceleration
Area under graph line = distance travelled in that time interval


What is gravity

Gravitational force is the force of attraction between all masses
Gravity attracts all masses but only noticed when one mass is really big eg planet and anything near a planet or star is strongly attracted


What are the important effects of gravity

1. On a planet surface all things accelerate towards the ground
2. It gives everything a weight


What is weight?
What is mass?

Not the same
Mass is amount of stuff in an object - same value anywhere
Weight caused by pull of gravitational force pulling towards earth
An object has same mass on earth as on moon but weight will be different because gravity on moon is less (it is smaller)
Weight measured in Newtons using a spring balance or newton meter
Mass is not a force measured in kgs with mass balance eg scales


What is the formula for mass, weight and gravity?
Example - what is weight of a 5kg mass on earth and on moon?

Weight=mass x gravitational field strength
W=m x g
Example: w=m x g
Earth: w= 5 x 10 = 50N
Moon: w=5 x 1.6 = 8N


What is the rule about acceleration due to gravity and gravitational field strength?

They are always the same no matter what planet you are on


What does a resultant force mean?
If a car has a driving force of 1000N but has air resistance of 600N what is resultant force?
Will the car's velocity change

A change in velocity
An object will change its state of rest or motion
Resultant force. 1000N - 600N = 400N
The car's velocity changes


Explain how an object moves

If the resultant force on a stationary object is zero, the object will remain stationary
There has to be a resultant force to start moving an object
No resultant force means no change in velocity
To keep going at the same speed needs zero resultant force


What effect is resultant force on acceleration?
What are the 5 forms of acceleration?

A non zero resultant force causes object to accelerate in direction of the force
Acceleration has 5 forms: starting, stopping, speeding up, slowing down and changing direction


Why don't objects in space need a driving force to move at constant speed

Steady speed means zero resultant force
On earth we have friction and air resistance so need a driving to keep things travelling at constant speed