A.2 Forces and Momentum

Question 1

Are forces vector or scalar

Answer 1

Vector

Question 2

Resultant force

Answer 2

The sum of all the forces acting on an object (using force triangle thing)

Question 3

Resolving forces

Answer 3

A force broken down into its two components at 90° to each other

Question 4

Newtons first law

Answer 4

“an object continues in uniform motion in a straight line or at rest unless a resultant external force acts”

basically: no resultant force= no acceleration and resultant force= accel

Question 5

Transitional Equilibrium

Answer 5

When an object is not accelerating due to having a resultant force of 0

Question 6

Newtons Second law

Answer 6

“The resultant force on an object is proportional to the acceleration providing mass of the object remains constant” (F=ma)

Question 7

Newtons Third law

Answer 7

“For every action on one object there is an equal but opposite reaction on another object”
basically: forces come in pairs (will be same between same objects)

Question 8

Contact forces

Answer 8

Forces that require objects to be in physical contact

Question 9

Field Forces

Answer 9

Forces that can act at a distance

Question 10

Normal force

Answer 10

Force perpendicular (90°) to the surface which an object is pushing on. Due to N3L the surface pushes back on the object (normal force).

Question 11

What is the net force at a constant speed?

Answer 11

0

Question 12

Static friction

Answer 12

Occurs when there is no relative motion between the two surfaces

Question 13

Dynamic friction

Answer 13

Occurs when there is relative motion between the two surfaces.

Question 14

Surface friction

Answer 14

The force that opposes the relative motion between the surfaces of two solid objects. Produced because on a microscopic scale the two surfaces are not completely smooth.

Question 15

Is dynamic friction affected by the speed between the two objects?

Answer 15

No, it is independent

Question 16

Other names for viscous drag force

Answer 16

In air- air resistance
In fluids- drag

Question 17

Factors effecting size of the drag force

Answer 17

• size and shape of object
• cross sectional area of object (widest point
• nature of the objects surface
• its speed
• the nature of the fluid it is travelling through

Question 18

Viscosity

Answer 18

Resistance of a fluid to movement through it. Measured in Pa s (pascal seconds). Also effected by temp.

Question 19

Viscous Drag

Answer 19

The drag force acting on a moving object due to the viscosity for the fluid through which it is moving.

Question 20

What situation does stokes law apply.

Answer 20

When the object is a small smooth sphere

Question 21

Buoyancy

Answer 21

The ability of a fluid to provide a vertical upwards force on an object placed in, or on, it.

Question 22

What is buoyancy effected by?

Answer 22

The density of the fluid (greater the density, larger the FB).

Question 23

What is the size of the buoyancy force equal to?

Answer 23

The weight of the fluid displaced.

Question 24

What are the vertical forces acting on a falling object?

Answer 24

Weight force (downwards, constant)
Buoyancy (upwards, constant)
Viscous drag (upwards, increases as speed increases)

Question 25

Terminal Velocity

Answer 25

When upwards and downwards forces on a falling object are balanced and it is falling at a constant speed.

Question 26

Tension force

Answer 26

A pulling force. May cause an object to stretch.

Question 27

Elastic restoring force

Answer 27

The magnitude of the restoring force used to return a stretched object to its original size. It is proportional to the extension.

Question 28

Spring constant

Answer 28

A value that represents the stiffness of the object.

Question 29

Why is there a negative sign in the elastic restoring force formula?

Answer 29

Because the FH acting in the opposite direction to the extension (the way it was stretched).

Question 30

Elastic limit

Answer 30

The maximum extension beyond which it becomes permanently deformed.

Question 31

What is a field?

Answer 31

A region of space where an object may experience a force due to a property such as mass or charge. (do not require physical contact)

Question 32

Gravitational field

Answer 32

Region of space where an object experiences a force (gravity) due to its mass

Question 33

What occurs due to unbalanced forces?

Answer 33

Acceleration

Question 34

What does it mean when an object is in equilibrium?

Answer 34

Net/resultant force is equal to 0

Question 35

Linear Momentum

Answer 35

The product of mass and velocity of an object.

Question 36

Is linear momentum a scalar or vector?

Answer 36

Vector

Question 37

What causes linear momentum of an object to change?

Answer 37

A resultant external force acting upon it. We say an impulse has been applied to the object equal to the change in momentum of the object.

Question 38

How can impulse be found from a graph?

Answer 38

It is equal to the area below a force-time graph.

Question 39

The law of conservation of momentum

Answer 39

"The total linear momentum of a system remains constant provided no external force acts on the system"

Question 40

A system

Answer 40

A group of objects (usually 2)

Question 41

Elastic collisions

Answer 41

No kinetic energy is lost (in reality only occurs between sub-atomic particles)

Question 42

What is conserved in collisions?

Answer 42

Linear momentum and energy (though energy may be converted to another form)

Question 43

Inelastic collisions

Answer 43

Some kinetic energy is lost and converted to heat and sound. Total energy still remains constant.

Question 44

Explosions

Answer 44

Can be treated as collisions though kinetic energy will always increase as it comes from the energy source of the explosion eg chemical potential

Question 45

Angular displacement

Answer 45

The angle through which an object undergoing circular motion will have moved through between points A and B

Question 46

Converting from rads to degs

Answer 46

x 180/pi

Question 47

Converting from degs to rads

Answer 47

x pi/180

Question 48

Period of circular motion

Answer 48

Time taken for one revolution

Question 49

Frequency of circular motion

Answer 49

The number of revolutions per second

Question 50

True or false: An object moving along a circular path at a constant speed is accelerating

Answer 50

true

Question 51

Centripetal Force

Answer 51

The unbalanced force that acts to create circular motion. Always cats towards the centre of the circle.

Question 52

How are the forces on an object balanced/ unbalanced when undergoing horizontal circular motion?

Answer 52

- vertical forces are balanced - horizontal are unbalanced towards the centre of the circle

Question 53

Where does centripetal force come from on banked corners?

Answer 53

The horizontal component of the normal force.

Question 54

Differences between vertical and horizontal circular motion

Answer 54

in vertical: - size of FN acting on the object varies throughout motion - speed of object may or may not be constant

Question 55

Forces acting on an object undergoing vertical circular motion at the top of the loop

Answer 55

Gravity and the normal force, both acting downwards. The slower the object the smaller FN.

Question 56

Forces acting on an object undergoing vertical circular motion at the bottom of the loop

Answer 56

Gravity downwards, the normal force upwards. Normal force> gravity. Centripetal force acts upwards and is the difference between FN and FG.

Question 57

What is normal force replaced with in situations where a mass is undergoing circular motion on a string?

Answer 57

Tension force