Chapter 4 - Force, Mass And Weight Flashcards
What is mass ?
The mass of an object is one of its physical properties and it depends on the amount of matter it contains
What happens if a resultant (net) force acts on a object ?
A resultant force acting on a object will make he object accelerate in the direction of the resultant force.
What’s the equation for net force ?
Force = mass x acceleration
What’s force measured in ?
N
What’s mass measured in ?
Kg
What’s acceleration measured in ?
ms-2
What does weight mean ?
The weight of an object on the surface of earth is the gravitational force acting on it
What’s the SI unit for weight ?
Kgms-2
What’s the equation for weight ?
W = mg
What’s the acceleration of an object in free fall ?
9.81 ms-2
What is friction ?
The force that arises when two surfaces rub against each other
What is drag ?
The resistive force on an object travelling through a fluid, the same as friction
What is tension ?
The force within a stretched cable or rope
What is upthrust ?
An upward buoyancy force acting on a object when it is in a fluid
What is a normal contact force ?
A force arising when one object rests against another object
What does a object that is moving through a fluid experience ?
It experiences a drag force from the liquid and drag is a frictional force that opposes the motion of the object
What contributes to the magnitude of a drag force ?
The magnitude of a drag force depends on several factors: speed of the object, shape of the object, the roughness/texture of the object and the density through which it travels.
The 2 most important factors that affect the magnitude of the drag force are the speed of the object and its cross-sectional area
Large cross sectional areas result in a greater drag force
For most objects, drag force is directly proportional to …
Speed squared
For e.g. if the speed is doubled then the drag force would increase by a factor of 4 and if the speed was tripled then the drag force would increase by a factor of 9
The drag force experienced by objects moving in the air is called …
Air resistance
What do lots of modern vehicles have to reduce drag ? And what does it do ?
Modern vehicles have smooth, streamlined shapes to reduce air resistance exerted against them while they are travelling. This increases the top speed of the vehicle and also reduces the amount of fuel used on a journey
During a vertical fall through air or another fluid, what happens to the weight of the object ?
the weight of the object stays constant
During a vertical fall through air or another fluid, what happens to the drag force as the speed of the object increases ?
The drag force increases as the speed of the object increases
What happens to the drag force the instant an object starts to fall ?
At the instant an object falls, there is no drag force on the object. The total drag force is equal to the weight.
What happens as the object falls?
As the object falls, the speed increases and this in turn increases the magnitude of the opposing drag force. The resultant force on the object also decreases and after a while the object will reach terminal velocity
What is terminal velocity ?
It is when the drag force on the object is equal and opposite to the weight. At terminal velocity, the object has zero acceleration and its speed is constant
Whats the full velocity time graph for a object falling through the air ?
The instant the object starts to fall, there is no drag force on the object and the object accelerates. as the object falls, the speed increases so the opposing drag force also increases. Eventually the object reaches terminal velocity - when. The drag force is equal/opposite to weight and the objects speed is constant and the acceleration of the object is zero
What’s a moment ?
A moment is the turning effect of a force
Whats the equation for a moment ?
Moment = force x perpendicular distance from the pivot
What will a moment act around ?
A moment will act around a pivot and a moment can act clockwise and anti-clockwise
Whats a moment measured in
Nm
Whats equilibrium ?
If we add up all the forces acting on a object and the resultant force is zero then the object is in equilibrium
F1 x d1 =
F2 x d2
What is a couple ?
A couple is defined as two equal and opposite forces acting on a body but on different lines of action.
The moment of a couple = force × perpendicular distance between the line of action of the forces
What must happen in order for an object to be stable ? And what can you do to improve stability ?
In order for an object to be stable, the centre of mass must be over it’s base
To improve your stability:
- widen the base
- lower the centre of mass
Torque means…
Turning force
What’s density ?
Density is the mass of a substance for a given volume
What type of property is density ?
Density is an intrinsic property - It is the same value for all objects made of that material
1ml =
1cm 3
What’s 1m2 in cm 2
10,000cm2
What’s 1m3 in cm3 ?
1,000,000 cm3