# Homework Help: Baby's fall.

1. Oct 28, 2012

### peripatein

Hi,

If a baby learning how to walk loses balance and falls sideways from an upright position (whilst standing), how long before the baby hits the ground, i.e how much time does one have to catch the baby?
Is the time in that case still equal to SQRT(2*baby's height/9.81)?

2. Oct 28, 2012

### CWatters

I think an assumption would have to be made about it's starting position.

If the baby happened to be standing perfectly straight up when it started to fall there would be no force pulling it over. So as it's starting position tends towards vertical the time taken to fall appears to approach infinity.

3. Oct 28, 2012

### CWatters

4. Oct 28, 2012

### peripatein

The question is formulated thus: "a baby learning how to walk loses balance and falls aside (from an upright position). Which parameters determine the time of its fall?" Should I use energy conservation instead, i.e potential equals kinetic, and then Vt = 1/2*g*t^2, for finding t?

5. Oct 28, 2012

### CWatters

As I said. If the baby is dead upright, why would it fall? What is the force pulling it sideways? Gravity only acts downwards.

Perhaps try drawing the set up. Assume baby is hinged to the floor at his feet. Have him leaning at say 10 degrees. Assume gravity acts on his center of mass. Work out the force causing him to rotate about his feet. What happens to that force as the starting angle approaches zero?

6. Oct 28, 2012

### CWatters

PS Using KE=PE to calculate the velocity with which he hits the floor is possible but calculating the time taken is a harder problem.

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