P8 -forces

Question 1

What is a scalar quantity

Answer 1

A scalar quantity is a quantity with a magnitude but no direction

Question 2

What is a vector quantity

Answer 2

A vector quantity is a quantity with a magnitude and a direction

Question 3

How can a vector quantity be represented

Answer 3

A vector quantity can be represented by an arrow. The length of the arrow represents the magnitude of the vector and the direction of the arrow represents the direction of the vector

Question 4

What is a force

Answer 4

A force is a push or pull on an object caused by it interacting with another object

Question 5

What is a contact force

Answer 5

A contact force is a force that acts when the two objects are touching each other

Contact forces: friction , air resistance , tension and a normal contact force

Question 6

What is a non contact force

Answer 6

A non contact force is a force that acts when the objects are separated

Examples:magnetic force , electrostatic force , gravitational force

Question 7

What is newtons third law of motion.

Answer 7

When two objects interact they exert equal and opposite forces on each other

E.g if a chair exerts a force of 100 N on the ground the ground will exert 100 N back

Question 8

What is mass

Answer 8

Mass is the amount of stuff in an object . It will be the same anywhere

Question 9

What is weight

Answer 9

Weight is the force acting on an object (on a mass)due to gravity . It will vary depending on where you are because the gravitational field strength changes depending on the area

For example your wieght on the moon will be lower than on the earth because the gravitational field strength is lower

Question 10

What is the equation that links mass and weight and gravitational field strength

Answer 10

Weight(N) = mass (kg)x Gravitational field strength

Question 11

What is the correlation between weight and mass

Answer 11

Weight and mass are in direct proportion .As one goes up the other also goes up by the same amount

E.g if the mass doubles ,the weight doubles as well

Question 12

What is a resultant force

Answer 12

A resultant force is a single force that has the same affect as a number of forces on a single pount

Question 13

What happens when a force moves an object

Answer 13

When a force moves an object through a distance work is done and energy is transferred

(The force does work to move the object and energy is transformed from one store to another )

Question 14

What happens when work is done against the frictional force

Answer 14

• When something is pushed along a rough surface work is done against frictional forces.
• Energy is transferred to the kinetic energy store of the object because it starts moving
• some energy also being transferred to the thermal energy store due to the friction . This creates an overall increase in the temperature of the object ( like when you rub your hands together )

Question 15

What is the equation for work done

Answer 15

Work done = Force (N) x Distance (m)(That the object moves through)

W=FxS

Question 16

How do you convert joules into newton metres

Answer 16

One joule = One newtonmetre 1J= 1Nm

-One joule of work is done when a force of one newton causes an object to move one metre

Question 17

What may happen ifyou apply a force to an object

Answer 17

It may stretch ,bend or compress

Question 18

Why do you need more than one force acting on the object to do this

Answer 18

You need more than one force acting in the object because otherwise the object would just move in the direction of the one applied force

Question 19

How can you tell if an object has been elastically or inelastically deformed

Answer 19

• If an object has been elastically deformed it will return to its original shape and length after the force has been removed
• If an object has been inelastically deformed it will not return to its original shape and length after the force has been removed

Question 20

What happens when a force stretches or compresses an object

Answer 20

• When a force stretches or compresses an object work is done ,energy is transferred to the elastic potential energy store
• The work done on the spring is equal to the amount of energy stored in the elastic potential energy store

Question 21

What is the equation linking force , extension and spring constant

Answer 21

Force= extension x spring constant

Question 22

What is the relationship between force and extension

Answer 22

Force and extension are directly proportional

As the force on the spring increases so does the amount the spring extends

-But there is a limit of proportionality where after that point the spring is no longer directly proportional to the extension

Question 23

What is the equation linking elastic potential energy store, spring constant and extension

Answer 23

Elastic potential energy = 1/2 spring constant x extension^2

This can be used to calculate the amount if energy stored in the springs potential energy store and how much energy is transferred to the spring as its defirmed

Question 24

What is a moment

Answer 24

A moment is the turning effect of a force

Question 25

What is the equation that links moments , force and distance

Answer 25

Moment = force x distance to pivot

Question 26

What has to happen for an object to be balanced

Answer 26

For an object to be balanced the sum of anticlockwise moments has to equal the sum of clockwise moments

Question 27

How do levers make it easier to do work

Answer 27

Levers increase the distance to pivot which means less force needs to be applied to produce the same moment

Levers act as force multipliers as they reduce the amount of force needed to complete tasks

Question 28

What do gears do

Answer 28

Gers interlock their teeth with other gears so that one tuening causes another to turn in the opposite direction

-They are used to transmit the rotational effect of a force

Question 29

How does the size of the gear impact the moment it will produce

Answer 29

• A force transmitted to a bigger gear will cause a greater moment because there is a greater distance to pivot
• A bigger gear will turn slower than a smaller gear though as there is a greater distance to pivot
• moment=force x gear radius

Question 30

What is the equation that links force,extension and spring constant

Answer 30

Force (N) = extension(m) x spring constant (N/m)

Question 31

What is the centre of mass

Answer 31

The centre of mass is a point where you can assume all the mass of an object is concentrated

Question 32

Always convert cm to m

Answer 32

Always convert cm to m

Question 33

How do you find out the vertical and horizontal components of a force

Answer 33

1. Decide on a scale for your drawing
2. Draw a dot to represent the object the force is acting on
3. Draw faint horizontal and vertical axis from the objects
4. Use a protractor to measure the angle from the horizontal
5. Use a ruler to draw the force from that angle (using the set scale)
6. Draw dotted lines from the head of the force vector to the horizontal and vertical axis
7. Draw horizontal and verticle components at the point where the dotted lines meet the horizontal and verticle axis
8. use a ruler to determine the magnitude of the horizontal and vertivle axis

Question 34

Where will a suspended objects centre of mass be

Answer 34

A suspended objects centre of mass will be directley below the point of suspension

Question 35

What will cause an object to topple

Answer 35

An object will topple if its line of action falls outside its base

Question 36

What will cause an object to stay stable

Answer 36

• An object will stay stable if its line of action falls with in its base
• Even if the object tilts , as long as its line of action falls within its base it will stay stable