Newtons Laws Flashcards
Newton’s First Law
INERTIA!
An object at rest will remain at rest unless acted on by an unbalanced force and an object travelling with a constant speed in a straight line will continue to do so unless acted on by an unbalanced force.
Newton’s Second Law
The acceleration of an object is directly proportional to the unbalanced force applied.
Newton’s Third Law
For every action force F1 There is an equal but opposite reaction force F2.
F1 = -F2
Average speed formula
v = s /t t = s / v s = vt
Kmh-1 to ms-1
divide by 3.6
ms-1 to kmh-1
times by 3.6
Acceleration formula
a = v - v0 / t a = acceleration v = final speed v0 = initial speed t = time
v = v0 + at t = v - v0 / a
Newton’s second Law formula
> Fres = ma
> Don’t forget to say LEFT or RIGHT in some
Another way of writing Newton’s second law…..
Fres = ^p / ^t
Physics of the airbag
When a car undergoes a front end collision, the airbag explosively inflates so that it is fully inflated in front of the driver before the driver reaches it
The face of the driver pushes into the airbag causing it to deflate “slowly”
This increases the time it takes for their face to come to rest and therefore reduces the force on their face
Increasing time it takes to come to rest
If a netball is thrown across the court at another players chest with strong force the player will catch it with two hands and to increase the time the netball takes to come to rest the player will catch the ball in front of their chest and swing their arms backwards in one swift movement, reducing the momentum of the ball and force needed to bring its movement to rest.
Decrease the time it takes to come to rest
If a wood chopper is using an axe to cut wood, to be able to slice it straight threw the wood chopper has to swing the axe with lots of force, therefore reducing the time it takes for the axe to come to rest.
Newton’s third law helicopter example
F1 is the blades pushing the air down and F2 is the air pushing the blades up.
Skaters example
Part 1 is Newton’s 1st Law (at rest until acted on)
Part 2 is Newton’s 2nd Law (larger force applies, larger acceleration)
- large mass is a smaller acceleration and small mass is larger acceleration
- F = mA = Ma
The whole image put together is Newton’s 3rd Law (opposite reactions)
What does the crumple zone do ?
The crumple zone increases the time to come to rest. Thus the force needed to bring the passenger to rest is reduced. So the chances of injury are reduced and force is also reduced.
Why seatbelt?
In a head on collision the car stops but the passenger continues at the same speed and hits the inside of the car increasing injury. If the seatbelt is on it provides the unbalanced force to stop the passenger. It applies a force over the robust parts of the body (hips & sternum) ie less injury.
Distance ( s ) is what ?
Is a measure of how far something is away from something else and is measured in metres ( m )
Displacement ( š ) is
The distance travelled in a certain direction from a given reference point
Eg: we have all gone to Victoria square
12.4km northeast from sacred heart college
Motion graphs always have ( t ) on the horizontal axis
Positive slope: constant speed AWAY from the reference point Negative slope: constant speed TOWARDS the reference point No slope (horizontal): at rest away from the reference point
A straight diagonal s vs t graph represents CONSTANT SPEED
The steeper the graph the greater the speed
Work
> Work ( W ) is done whenever a force ( F ) acts on an object and that object moves a distance ( s ) in the direction of that force
Work is measured in JOULES
W = Fs
Weight
> A FORCE measured in NEWTONS ( N )
Weight ( wt ) is the product of mass ( m ) of an object and the acceleration ( g ) due to gravity
wt = mg
> wt = weight ( N )
m = mass ( kg )
g = acceleration due to gravity ( ms-2)
9.8 ms-2
Headrest
- Consider a passenger at rest in a stationary car without a headrest. When the car is hit from behind an unbalanced force is provided the seat that pushes the passengers body forwards. The head remains at rest. Until the neck provides the unbalanced force needed to make it catch up with the body. This can cause neck injury or death.
- A headrest provides the unbalanced force that causes the head to move forward at the same time the body does, thus avoiding injury.