Tag Archives: children

The physics of maiming a child (repost because of another close encounter)

Dear Driver,

When you backed out of a driveway and did not even see how I swerved around behind your car to avoid T-boning you, how dare you have the temerity to tell me you were careful!  I was 7 feet tall, dressed in bright yellow and traveling at no more than 10 km/h.  Perhaps a simple lesson in physics will help you and your fellow “driveway backers” to realise how dangerous you are and to adopt safer driving practices.

In the diagram you can see a car backing out of a driveway.  Typically when you are at the edge of your property and have a fence (see photo below) blocking your view of the footpath you are able to see about 1.7 metres along the footpath.  Let us imagine that there is a child on a trike riding at 5 km/h just out of your line of sight.  How long  does it take them to travel that 1.67 metres?  The physics is quite easy.

Car backing out of a driveway. Illustration of how little of the footpath can be observed.

Car backing out of a driveway. Illustration of how little of the footpath can be observed.

Velocity = distance/time, therefore time = distance/Velocity.

5 km/h is 5000 metres in 60 x 60 seconds, ie about 1.4 m/s.  Putting this in the formula above means that it takes about 1.2 seconds for the child to travel that 1.67 metres.

Now consider this. According to design guidelines for safe bicycle use 2.5 seconds must be allowed for someone to observe the danger, react, apply brakes and stop.  In other words, if you covered the distance from your driveway to the middle of the footpath, about 1 metre, in under 1.2 seconds you will almost certainly hit the child.  That is a speed of just 3 km/h!!!!!

Now consider who else is on the footpath, all legally:

  • Pedestrians 5 km/h
  • Joggers 5- 15 km/h
  • Kids on skateboards or scooters 10 km/h
  • Child on bicycle with small wheels, 10 km/h
  • Mobility scooter, 5-10 km/h
  • Me on my Trikke, 10 km/h
  • Postie on a bike 5-10 km/h.

For those going 10 km/h your speed needs to be just over 1.5 km/h to hit someone!

So, before you do some damage here is what you can do:

  • Never back out of a driveway unless you really really must.  If you think you must because of the design of your driveway, change the design!
  • Cut back those hedges, remove some of that fence so that you can see further.
  • Always always always stop at the end of your driveway (BEFORE THE FOOTPATH) and toot a horn.  Then proceed very very slowly.

By the way, you are legally obliged to give way:

 Land Transport (Road User) Rule 2004

4.4 Giving way when entering or exiting driveway

(1)
A driver entering or exiting a driveway must give way to a road user on a footpath, cycle path, or shared path (as described by clause 11.1A(1)).

Thank you for considering the physics of maiming a child, may you never find your self in such a terrible situation.

Regards,

Dr John Pickering

A typical driveway with almost non-existant visibility

A typical driveway with almost non-existent visibility

———

Feature Image: Intangible Arts https://www.flickr.com/photos/intangible/ under Creative Commons Attribution 2.0 licence.

Let the children take us to space

44 years ago a feather and a hammer were dropped at the same time on the moon by Commander David Scott of Apollo 15. An experiment that continues to cause wonder and inspire children today. Indeed, it may well have been an experiment children would have dreamed up for the astronauts to do. This post is simply to get the children of New Zealand thinking of experiments and possibilities once more.

We are going to have a rocket launch facility in our own backyard.  Wow!  If that doesn’t excite, then little will.  Rocket Lab inspires not just because big controlled explosions are cool (well duh!), but because those involved are innovative, and commercially savvy. Exactly the qualities I’d like to see fostered in the next generation.

Peter Beck, founder and CEO of Rocket Lab has promised that anyone can reach space.  Well said Peter. Here’s my vision to add to his.

  • Let that anyone be the children of New Zealand.
  • Let New Zealanders launch our first satellite (#NZS1 for want of a better handle)
  • Let that satellite be locally dreamed up and grown
  • Let there be a competition to gather ideas for what NZS1 should do
  • Let our children vote on which idea they’d like to see launched first
  • Let the money be crowd-sourced from within New Zealand (less than $2 each!).
Rocket Lab's vision for their launch facility (used with permission)

Rocket Lab’s vision for their launch facility (used with permission: http://www.rocketlabusa.com)

R_014 R_011

 

The physics of maiming a child

Dear driver,

When you backed out of a driveway and did not even see how I swerved around behind your car to avoid T-boning you, how dare you have the temerity to tell me you were careful!  I was 7 feet tall, dressed in bright yellow and traveling at no more than 10 km/h.  Perhaps a simple lesson in physics will help you and your fellow “driveway backers” to realise how dangerous you are and to adopt safer driving practices.

In the diagram you can see a car backing out of a driveway.  Typically when you are at the edge of your property and have a fence (see photo below) blocking your view of the footpath you are able to see about 1.7 metres along the footpath.  Let us imagine that there is a child on a trike riding at 5 km/h just out of your line of sight.  How long  does it take them to travel that 1.67 metres?  The physics is quite easy.

Car backing out of a driveway.  Illustration of how little of the footpath can be observed.

Car backing out of a driveway. Illustration of how little of the footpath can be observed.

Velocity = distance/time, therefore time = distance/Velocity.

5 km/h is 5000 metres in 60 x 60 seconds, ie about 1.4 m/s.  Putting this in the formula above means that it takes about 1.2 seconds for the child to travel that 1.67 metres.

Now consider this. According to design guidelines for safe bicycle use 2.5 seconds must be allowed for someone to observe the danger, react, apply brakes and stop.  In other words, if you covered the distance from your driveway to the middle of the footpath, about 1 metre, in under 1.2 seconds you will almost certainly hit the child.  That is a speed of just 3 km/h!!!!!

Now consider who else is on the footpath, all legally:

  • Pedestrians 5 km/h
  • Joggers 5- 15 km/h
  • Kids on skateboards or scooters 10 km/h
  • Child on bicycle with small wheels, 10 km/h
  • Mobility scooter, 5-10 km/h
  • Me on my Trikke, 10 km/h
  • Postie on a bike 5-10 km/h.

For those going 10 km/h your speed needs to be just over 1.5 km/h to hit someone!

So, before you do some damage here is what you can do:

  • Never back out of a driveway unless you really really must.  If you think you must because of the design of your driveway, change the design!
  • Cut back those hedges, remove some of that fence so that you can see further.
  • Always always always stop at the end of your driveway (BEFORE THE FOOTPATH) and toot a horn.  Then proceed very very slowly.

By the way, you are legally obliged to give way:

 Land Transport (Road User) Rule 2004

4.4 Giving way when entering or exiting driveway

(1)
A driver entering or exiting a driveway must give way to a road user on a footpath, cycle path, or shared path (as described by clause 11.1A(1)).

Thank you for considering the physics of maiming a child, may you never find your self in such a terrible situation.

Regards,

Dr John Pickering

A typical driveway with almost non-existant visibility

A typical driveway with almost non-existent visibility

Children killed by mothers – duh!

The media is in a tiz over a police report stating that 45% of children killed in family violence were killed by their mothers.  The Herald says “Children are far more likely to be killed by their mothers than any other category of offender,”; Newstalk ZB reports Bob McCoskrie as saying this is “startling”; Stuff ramp it up a bit and begin “Nearly 50 per cent of children who die as a result of family violence are killed by their mothers.”

Well, duh!  Don’t they know that children are far more likely to be living with their mothers than any other adult?  The “any other category of offender” the Herald talks about include Fathers, Stepfathers, Boyfriends, Grandmothers, and various others.  Given there were 33 deaths looked at this is a large number of groups to try and analyse.  For the numbers to have any meaning they need to assess the numbers using what are called “case controls.” For example, if they looked at other factors, eg socio-economic, and then assessed the make up of households in that group they may find that children in that group are living predominantly with their mothers and much less with Fathers, Stepfathers, boyfriends etc.  The numbers may only reflect who they are living with, not some kind of “evil mother” syndrome.

What use, really is such a report?  How will it help prevent further deaths?  I suspect the answers are “little” and “it won’t” but this will not prevent endless ours of hand wringing in the media.  Surely, we can do better.