2007-06-27 09:20:23 · 10 answers · asked by snstv_lion 1 in Science & Mathematics ➔ Physics
As you push on the truck, an equal and opposite force of friction from the tires' contact with the ground pushes back in the opposite direction. Keep in mind his other 2 laws.
- The second law states that:
Σ F = ma
So, if you push with a force P in the positive direction, the friction force f will push in the negative direction such that it cancels out your force:
P - f = ma = 0
==> this means that acceleration is still zero
- The 3rd Law states "for every action, there is an equal and opposite reaction." This explains why the force of friction pushes against your applied force. So, the harder you push, the harder friction pushes back. You would need to push harder than the maximum friction force to get the truck to move. In fact, I can tell you roughly how hard:
f(max) = μN, where μ is the coefficient of friction and N is the normal force. Because the normal force cancels out the weight (Newton's 3rd again), the maximum friction will be equal to μ*W, where W is weight.
Now, for a rubber tire on asphalt or concrete, values of μ will be somewhere .5 and .85. So, if the truck weights 1 ton, this is 2000 lbs. Therefore, the maximum friction force will be somewhere between .5*2000 lb and .85*2000 lb, so your push would need to be at least 1000 lb and possibly as high as 1700 lb. You can't actually push that hard, can you?
2007-06-27 09:23:25 · answer #1 · answered by C-Wryte 3 · 1⤊ 0⤋
Friction. The rolling resistance of the tires on the ground must be overcome for the truck to begin to move. It has nothing to do with inertia. The inertia only will control how fast I can accelerate the truck once I am pushing hard enough to overcome friction. If you remove all friction of the system, the truck will begin to roll immediately regardless of the size (inertia) of the truck. A small truck will seem easier to push because it will not take as much force to get it going the same speed as a larger truck would.
*** Note that the discussion given by the first aswerer is correct, however not complete. The value he is computing is the force necessary to overcome sliding friction to make the truck physically slide across the ground WITHOUT the tires rotating so is conservative. In reality it would take less force than this because once the internal friction of the system (bearings, etc) is overcome the wheels will roll and surface friction on the road is less.***
2007-06-27 16:43:20 · answer #2 · answered by Anonymous · 1⤊ 0⤋
That's not right. According to Newton's First Law, the truck will only move IF the force exerted on it exceeds the force holding it in place.
The truck has so much mass and therefore inertia, it will take a great deal of force to overcome it's (*other part of Newton's First Law)*) desire to stay put.
2007-06-27 16:25:47 · answer #3 · answered by Anonymous · 1⤊ 0⤋
I think you're too smart to leave the brakes on, and as others have said, inertia doesn't play a part. However, many brake systems have a "light" residual drag even when not applied. Tire rolling resistance is certainly a key cause, and there are also irregularities in the road which can increase resistance much more if big enough to raise the truck, even a little. Also consider wheel bearing and drive axle friction; small when running, larger when stopped due to loss of dynamic lubrication.
2007-06-27 17:45:52 · answer #4 · answered by kirchwey 7 · 1⤊ 0⤋
Newton's 1st Law states that an object stays in a constant state of motion unless a NET FORCE acts on it. You are pushing in the positive direction. There is something called static friction which is preventing the truck from moving (acting in the negative direction). Since your push force equals the force of static friction, there is no net force acting on the truck, meaning it will just sit there. If you were to push hard enough to overcome static friction, the truck would move.
2007-06-27 16:37:17 · answer #5 · answered by msi_cord 7 · 0⤊ 0⤋
Because you're not the only one who exerst a force of the truck. If the sum of all forces is still zero it's not going anywhere. The forces are: gravity (down) reaction from the pavement (up), you (forward), friction everywhere in the wheels (opposing the forward force). If you pull much harder you might be able to exceed the limit of friction, and the truck will move.
2007-06-27 16:26:53 · answer #6 · answered by Snowflake 7 · 1⤊ 0⤋
Pay close attention to the first law: the truck will only move if the force applied to it is higher than the force holding it back. Try adding more force.
2007-06-27 16:33:49 · answer #7 · answered by Anonymous · 0⤊ 0⤋
A..Insufficient force to overcome the Inertia of the truck.
i.e. Its mass and the static friction of the tyres on the road.
B..Its brakes are on.
C..Its brakes are on and its facing uphill and you're pushing from behind.
D..It's parked with the front end against a building and you're pushing from behind.
2007-06-27 16:26:26 · answer #8 · answered by Norrie 7 · 0⤊ 0⤋
The force you are exerting is not enough to overcome the inertia of the truck. See the second law of motion.
2007-06-27 16:24:47 · answer #9 · answered by JLynes 5 · 2⤊ 2⤋
you need to make enough force.
2007-06-27 16:28:44 · answer #10 · answered by nicole 1 · 0⤊ 0⤋