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Newton’s 2nd Law
In this lesson, we will be focusing on Newton’s 2nd Law of Motion2nd Law of Motion.
This law is all about the connections between forceforce, massmass, and accelerationacceleration.
Let’s find out more from the characters in Eureka.
3 2nd Law/Speed
The red ball has twice the mass of the blue ball
So.... to make them move at the same speed,
what must happen to the force?
2 kg1 kg1 X 2 X? ?
FORCE is proportional to MASSLet’s try some other masses…
3 kg3 kg
1 kg1 kg 6 kg6 kg1 X
3 X
6 X
20 kg20 kg20 X? ? ? ?
? ?
What if both balls have the same mass, but the speeds are different.
To double the speed, what must happen to the force?
1 kg1 kg1 X 2 X? ? 40 km/hr40 km/hr20 km/hr20 km/hr
So... FORCE is proportional to CHANGE OF SPEED....
1 X1 X
20 km/hr20 km/hr
1 kg1 X
20 km/hr20 km/hr
1 kg2 X
40 km/hr40 km/hr
1 kg3 X
60 km/hr60 km/hr
1 kg4 X
80 km/hr80 km/hr
? ?
? ? ? ?
The amount of forceforce needed depends on massmass AND change of speedchange of speed
Let’s sum up what we know so far…
If we double mass,we ______ force
If we double change of speedwe ______ force
Ready for a brain check?
doubledouble
doubledouble
1. If mass of an object increases, what must happen to amount of
force to move or stop it?
A. increasesB. decreases
C. stays the same
2. To increase the speed of an object, what must happen to the
amount of force?
A. increasesB. decreases
C. stays the same
4 Acceleration 1
Let’s look at this idea of change of change of speedspeed a little more…
The object starts out slowly, then goes faster, faster, faster…until it reaches
top speed.
Therefore, it’s all about how quickly it changes speed or the “raterate of change
of speed”.
The word that means “rate of change of speed”
is accelerationacceleration…
This means we can write
Newton’s 2nd Law as
“forceforce varies with massmass and accelerationacceleration”
The key idea of this Law can also be turned into an equation:
Force = mass x accelerationForce = mass x acceleration(F=maF=ma)
Fma Live 2nd Law
FMA Live!
Force = mass x accelerationForce = mass x accelerationF = maF = ma
In an equation, changing one variable means another variable must also change.
If... What happens to…F = m a F?
F = m a a?
Let’s try some more…
If... What happens to…1. F = m a a?
2. F = m a a?
3. F = m a F?
4. F = m a a?
Big soccer ball
Soccer Balls
Teacher in Wagon
Teachers
Slingshot
Slingshot
Space Station
Mini_bike
Mini Bike
