# Teacher's teachings are questionable

1. Jun 1, 2010

### poprocks4

I am currently in eighth grade science, in a physics/energy unit. My teacher does not seem to know what she is doing, and I question her knowledge of what she is teaching. Here are some of the formulas and theories she insists are true:

-force(N) =mass x 9.8m/s/s

-The force gravity exerts on objects is 9.8m/s/s

-one joule=force required to accelerate an object at 9.8m/s/s

Also she insists that air resistance has no effect OUTSIDE a vacuum

2. Jun 1, 2010

### PhanthomJay

I wasn't exposed to Physics until grade 11...the times they are a-changing...anyway, if you think these statements are false, how would you re-write them as true statements? And welcome to the Physics Forums.

3. Jun 1, 2010

### poprocks4

I would say that force=mass x acceleration (not nessesarily the acceleration of gravity though)

gravity accelerates objects at 9.8m/s/s

one joule=one newton/metre

air resistance has an effect outside a vacuum

Last edited: Jun 1, 2010
4. Jun 1, 2010

### pgardn

Most people my age did not get physics until High School at best. It was not required. General Science took into account some very shaky physics. There is so much on the internet now that if you want to, especially as an 8th grader, learn a heck of a lot on your own.

At least you dont have to rely on a new set of encyclopedias to find out what was going on like people a little older than I am.

Gravity has an effect inside a vacuum as well. Gravity does not stop acting in the absence of air. Now if the earth was to suddenly disappear...

5. Jun 1, 2010

### poprocks4

Its not the actual physics class, but a physics unit in a regular science class.
Also, i made some typos in my last post, which i edited; i meant to say air resistance instead of gravity. of course gravity has an effect inside a vacuum (:

6. Jun 1, 2010

### pgardn

It is possible your teacher was an education major or a life science major and physics was never taught to her properly so hang in there and visit this site.

You dont find many Physics majors wandering the streets looking for a job teaching science sadly to say. And you will find in years to come that there are some Physics types that know a heck of a lot about Physics, but have no idea how to make others understand it. What seems completely logical, intuitive and obvious to one person may be a sea of confusion to another. Good teachers usually have a good feel for what others find difficult and can ask appropriate questions that lead students to what is reasonable. My worst Physics teacher was probably one of the most valuable to the University due to his research.

7. Jun 1, 2010

### Pengwuino

Almost! The units for joule is newton*metre. The third one has a little caveat though, 1 joule is the energy required to supply a constant force of 1 Newton over a distance of 1 meter. That is how it is defined. What you stated is simply the dimensions of Joules (although multiplying instead of dividing).

Also, "gravity" accelerating objects at 9.8m/s^2 is only good for the surface of the Earth. If you get further out from the Earth, it changes. Likewise, on different planets the gravitational acceleration is different (notice how people who walked on the moon seemed to accelerate downward at a slower rate?).

8. Jun 1, 2010

### poprocks4

ok, so now do I tell the teacher she is teaching the class wrong or just let it go

9. Jun 1, 2010

### Integral

Staff Emeritus
With a lot of respect and in private, do NOT take the argument into the classroom.

10. Jun 1, 2010

### pgardn

+1...

11. Jun 2, 2010

### Ketman

You wrote "gravity" when you meant "air-resistance", which was a typo. But there is such a thing as verbal typos, you know. When you're saying a lot of things to a lot of people in a classroom, you're bound to make mistakes. I can easily imagine someone saying "the force is 9.8 m/sec^2" when they meant acceleration. You can go back and correct your typos, but she can't. On balance I don't think she's made any more false statements than you have yourself, e.g. saying a joule = newton/metre. Your own language isn't exact enough for you to be picking up on hers.

12. Jun 3, 2010

### ianprime0509

The first equation for force isn't the equation for force but rather for weight on Earth.

Your teacher's gravity formula only works on Earth, the full formula is:

$$F=\frac{Gm_{1}m_{2}}{d^2}$$

The Joule is the unit for work, and is defined as N*m. The force required to accelerate an object at 9.8m/s/s can be calculated using the formula F=ma.

Finally, the fourth statement is the opposite of what it should be: air resistance only has an effect where there is air (i.e. not in a vacuum)

13. Jun 9, 2010

### poprocks4

Sorry my english is not too good