Equillibrium & center of mass

• Natuurkunde
• Middelbare school
• vmbo lwoo
• Leerjaar 2,3

Equillibrium & center of mass

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You know how to determine the center of mass

You can explain the difference between stability and equillibrium

You can explain what to do to make something more stable

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Equillibrium

How is this possible?

How is this possible?

Can you try to explain the bird balancing on your finger?

How is this possible?

How is this possible?

Can you try to explain why this construction 

does not fall to the ground?

Center of mass

Every object has a center of mass. 

If the point of application of a force originates in the center of mass of an object, the object will follow a linear acceleration without an angular acceleration.

Simulation

Stability

An object could be in a state of equillibrium even if it is unstable.

A state of equillibrium is reached when all forces and moments equal each other out.

If an object is stable or unstable depends on how easy it is for the center of mass to get outside of the support area.

The higer the center of mass is situated and the smaller the support area, the more unstable an object will be.

Drag to the corresponding red box

MOST STABLE

in between

LEAST STABLE

A

B

C

Drag to the corresponding red box

EQUILLIBRIUM

NO EQUILLIBRIUM

A

B

C

So tell me

What do you need for a stable equillibrium?

Equillibrium 1

When all forces equal each other out.

The resultant force (also called netforce) = 0 N

The object will be in rest.

It either wil not move, or only move with a constant speed.

It wil not start to change its speed, direction or shape

Equillibrium 2

In both situations there is an equillibrium.

As you can see all forces equal each other out, 

since both boys have the same mass and are 

sitting at the same distance from the middle.

Equillibrium 3

There are situations possible in which there  is no 

equillibrium even though all forces equal each other out.

To have an equilibrium, not only all forces need to cancel

each other out, the rotational effects need to cancel 

each other out as well.

Equillibrium

Only when:

all forces canceleach oher out:

the resultant force =  0 N

And

all moments (the clockwise and anti clockwise rotational effect) 

cancel each other out. The resultant moment = 0 Nm

Equillibrium

1. Resultant force is zero  
   
2. Resultant moment is zero

keep in mind 

that:

stability is not the same as equillibrium

1. Low center of mass
   
2. Large support area
   
3. Large mass

Stability

Which object is more stable?

1. A
2. B

Three cans of coke.
The first is full.
The second has been emptied halfway.
The third is totally empty.
Which can is the most stable?

Challenge: Can you balance a can of coke on its side.

Make a photo if you succeeded.

An object tumbled over

Can you mention some causes?

Using that what you have just learned, can you explain why the Fosbury Flop makes you jump higher than before?