Yahoo 知識+ 將於 2021 年 5 月 4 日 (美國東岸時間) 停止服務。從 2021 年 4 月 20 日 (美國東岸時間) 起，Yahoo 知識+ 網站將轉為僅限瀏覽模式。其他 Yahoo 資產或服務，或你的 Yahoo 帳戶將不會有任何變更。你可以在此服務中心網頁進一步了解 Yahoo 知識+ 停止服務的事宜，以及了解如何下載你的資料。

Chauchau 發問於 科學及數學其他 - 科學 · 1 十年前

# toppling in Physics

If a car want to bend on a horizontal ground, only three force acts on the car. They are weight(exerted by the earth on the car), the normal reaction(exerted by the road on the car) and the lateral static friction(exerted by the road on the tyres). It can be seen that the normal reaction and the weight is in opposite direction and equal in magnitude, balancing each other and the lateral static friction is horizontal. If we take moment about the C.G. of the car, should the car topple? What can cause an object to topple?

### 2 個解答

• ?
Lv 7
1 十年前
最愛解答

When an object is in equilibrium, there are no net force and net moment acting on the object.

In the case of a car turning round a corner, the car is definitely NOT in equilibrium, it is in a state of motion. In fact, it is under an acceleration, which is the centripetal acceleration. As such, there must be a net force, and hence net moment, acting on the car.

A zero net force and zero net moment condition is only applicable to objects that are at rest or in uniform velocity.

2010-06-01 09:12:46 補充：

There is another explanation, which I think is more acceptable. There are two normal reactions, one acts on the tyres at the inward side of the car and the other on the tyres at the outward side....(cont'd)

2010-06-01 09:13:34 補充：

.... By taking moment at the centre of mass of the car, moment due to friction + normal reaction at the inward side balances the moment due to normal reaction at the outward side. Hence, you would see that the normal reaction at the outward side is larger than that at the inward side....(cont'd)

2010-06-01 09:14:10 補充：

.... This is a common experience that the car tends to incline towards the outward side when turning a bend.

• Chau
Lv 5
1 十年前

In face, the car should topple at some centripital force.As show in the picture, when the car is bending on a horizontal ground, the normal reaction is shipping to the right due since the car tend to topping outward. As a result, when the reaction become arrive the coner, it is no more place for it to ship more. Hence, this is the topping friction.In the above case, the car is a square, when fl=Rl,f=mg,the car will start to topple. Therefore, if the speed of the car is large enough to bend. The friction>mg,then the car will topple.

2010-06-01 22:04:35 補充：

What can cause an object to topple?

Net moment can cause it.As like as force, there must be a net force so that the object will accelerate.In the case of topping, a Net moment is required so that the object will topple.

資料來源： Lucas Chau