# Newton's First law - Dropping a feather and a hammer...

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1. May 13, 2015

### copypacer

<<Mentor note: Edited for language>>

1. The problem statement, all variables and given/known data

If I have a feather and a hammer and drop it at the same time from the same height (with out air resistance, so basically in a vacuum) Why would it land on the ground at the exact same time?

2. Relevant equations
F = ma

3. The attempt at a solution
My assumption is that with the equation posted above, which I think has nothing to do with why it drops at the same time, even though they both have different masses but the same acceleration.

- Also, would it accelerate because the only force is gravity (9.8)....but thats a force so would it be -9.8 = m*a ?

<<*edited*>> I'M SO CONFUSED

taking physics in college and i'm already in chapter 9 which is center mass and linear momentum, and just barely understanding force and motion which is chapter 5 while midterm is next tues <<*edited*>>

Last edited by a moderator: May 14, 2015
2. May 13, 2015

### SammyS

Staff Emeritus
You probably need to review some basic concepts. What is meant by each of the following?

acceleration

acceleration due to gravity.

Weight (of an object)

Last edited by a moderator: May 14, 2015
3. May 14, 2015

### copypacer

a feather and a hammer or anything heavier will have a different mass compared to the feather. Acceleration is 9.8 but the forces will be different because of different masses, basically i still don't see how they will end up on the ground at the same time due to different forces and different masses

4. May 14, 2015

### SammyS

Staff Emeritus
If acceleration is the same, and the initial velocity is the same, then the motion is the same, Right?

5. May 14, 2015

### copypacer

Right, but I thought the time it would get there would be different because the hammer would have a greater force because of its greater mass.

My guess is that because the hammer has a greater mass, that mass compensates for the greater force and essentially, the ratio of Force to mass is the same as for the feather. The ratio of force to mass which is acceleration is the same for the hammer as for the feather and that is why both of them land at the same time.

6. May 14, 2015

### SammyS

Staff Emeritus
Right. The ratio of force to mass is the same for both.

7. May 14, 2015

### copypacer

When you said "weight" do you mean mass?............but then again this is in respect to gravity right? confused

8. May 14, 2015

### SammyS

Staff Emeritus
No. Look in your textbook or notes for the definition of weight.

Weight is not the same as mass.

9. May 14, 2015

### toesockshoe

I have a question... isnt this more of a kinematics problem than a F=ma problem?

10. May 15, 2015

### copypacer

I know, weight has to do with gravity, BUT, we still call it mass because we need the measurement of matter in the object and than calculate the gravity in order to find the force.

Also, if I wanted to find what my mass is, do I just divide my weight by 9.8?

11. May 15, 2015

### SammyS

Staff Emeritus
Mass is a measure of an objects inertia.

Gravity is the force exerted on an object due to gravity.

An isolated object that is not in any gravitational field still has mass. The mass of that object is the same no matter how much gravity is present.