# Physics: Forces

Scalar Quantity
Scalar Quantities have magnitude (size) only.
1 of 37
Vector Quantity
Vector Quantites have magnitude and an associated direction.
2 of 37
How do you represent a Vector Quantity?
With an arrow. The length of the arrow represents the magnitude and the direction.
3 of 37
What is a force?
A push or a pull that acts on an object due to the interaction with another object.
4 of 37
Contact Forces
The objects are physically touching.
5 of 37
Non-Contact Forces
The objects are physically seperated.
6 of 37
What are examples of contact forces?
Friction, air resistance, tension and normal contact force.
7 of 37
What are examples of non-contact force?
Gravitational force, electrostatic force and magnetic force.
8 of 37
What quantity is force? Vector or Scalar?
Force is a vector quantity.
9 of 37
What happens when 2 objects interact?
When 2 objects interact, there is a force produced on both objects. An interaction pair is a forces that are equal and opposite and act on 2 interacting objects.
10 of 37
Example of what happens when 2 objects interact?
The sun and the Earth are attracted to each other by gravitational force. This is a non-contact force. An equal but opposite force of attraction is felt by both the sun and the Earth.
11 of 37
Weight
Weight is the force acting on an object due to gravity. The force of gravity close to the Earth is due to the gravitational field around the Earth.
12 of 37
What is the weight of the object dependent on?
The weight of an object depends on the gravitational field strength at the point where the object is.
13 of 37
What equation do you use to calculate weight?
weight = mass x gravitational field strength W=mxg (N)=(kg)x(N/kg)
14 of 37
What is the weight of an object considered as?
The weight of an object may be considered to act at a single point referred to as the object's 'centre of mass'.
15 of 37
Is the weight of an object and the mass directly or indirecttly proportional?
The weight of an object and the mas of an object are directly proportional.
16 of 37
How do you measure weight?
Weight is measured using a calibrated spring-balance (a Newtonmeter)
17 of 37
Resultant Force
A number of forces acting on an object may be replaced by a single force that has the same effect as all the original forces acting together. This singlle force is called the resultant force.
18 of 37
How do you calculate the resultant of 2 forces that act in a straight line?
Diagram
19 of 37
Give an example of a force acting on an isolated system.
Skydivers are an example of forces acting on an isolated system. The weight acts on the skydiver pulling him towards the ground and drag (air resistance) also acts on the skydiver in the opposite direction to his motion.
20 of 37
Show a free body diagram of a skydiver.
Diagram
21 of 37
How can a single force be resolved?
A single force can be resolved into 2 components acting at right angles to each other. The 2 component forces together have the same effect as the single force.
22 of 37
How do you use vector diagrams?
Diagram
23 of 37
Work Done
When a force causes an object to move through a distance work is done on the object. So a force does work when the force causes a displacement of the object.
24 of 37
What is the equation for work done?
workdone = force x distance moved along the line of action of the force W=Fxs (J)=(N)x(s)
25 of 37
When one joule of work is done what is the displacement?
1 Joule = 1 Newton meter
26 of 37
What energy transfers are involved when work is done?
When you push something along a rough surface you are doing work against frictional forces. Energy is being transferred to the kinetic energy store of the object because it starts moving, but some is also being transferred to thermal energy stores
27 of 37
continued...
due to the friction. This causes the overall temperature of the object to increase.
28 of 37
What happens you apply a force?
When you apply a force to an object you may cause it to bend, stretch or compress.
29 of 37
How do you do this?
You need more than one force acting on the object.
30 of 37
What does an object have to be to go back to its original form?
It is elastically deformed.
31 of 37
Inelastically deformed
Objects that don't returm to its original shape and length after the force has been removed.
32 of 37
How do you calculate force?
force = spring constant x extension F=Kxe (N)=(N/m)x(m)
33 of 37
Is the extension of an elastic object directly proportional?
Yes, the extension of an elastic object such as a spring is directly proportional to the force aplied, provided that the limit of proprtionality is not exceeded. This also applies to compression of an elatic object.
34 of 37
What happens when a force is stretched or compressed?
A force that stretches or compresses a spring does work and elastic potential energy is stored in the spring. Provided the spring is not inelastically deformed, the work done on the spring and the elastic potential energy stored are equal.
35 of 37
What does the graph show?
The graph shows force against extension for an elastic object. There is a maximum force when the graph curves showing when extension is no longer proportional.
36 of 37
How do you calculate work done in stretching (or compressing) a spring up to the limit of proportionality?
Elastic Potential Energy = 0.5 x spring constant x extenstion ^2 Ee=1/2ke^2
37 of 37

## Other cards in this set

### Card 2

#### Front

Vector Quantites have magnitude and an associated direction.

Vector Quantity

### Card 3

#### Front

With an arrow. The length of the arrow represents the magnitude and the direction.

### Card 4

#### Front

A push or a pull that acts on an object due to the interaction with another object.

### Card 5

#### Front

The objects are physically touching.