P5 - Forces and Motion

Speed=

distance/time.

Describe the effect of being tired on the braking distance of the car.

None

Define velocity

Speed in a particular direction.

What is a vector quantity?

A quantity that has both magnitude and direction.

What is a scalar quantity?

A quantity that has only magnitude

Acceleration==

Change in velocity / time taken

Acceleration unit

m/s^2

Velocity unit

m/s.

Gradient of a velocity time graph ==

acceleration

Resolution

Smallest change in a quantity that an instrument can detect/measure

Is velocity scalar or vector

Vector

Is speed scalar or vector

Scalar

Define force.

A push or pull classified as contact or non contact

What is Newton's 3rd law

If object A exerts a force on object B, then object B will exert and equal and opposite force on object A

What is Newton's 2nd law

Force = mass x acceleration (f=ma)

What is Newton's 1st law

An object will remain stationary or will travel at a constant velocity unless acted on by a resultant force.

Weight==

mass x gravitational field strength.

(In SUVAT) What does S stand for

Distance

(In SUVAT) What does U stand for

Initial velocity.

(In SUVAT) What does V stand for

Final velocity.

(In SUVAT) What does A stand for

Acceleration

(In SUVAT) What does T stand for

Time

If someone jumps out of a plane, which force never changes

Weight/gravitational force.

Define energy

the capacity to do work.

Work done =

force x distance

Work done unit

Joules (J).

Gravitational potential energy =

mass x gravitational field strength x height

Define gravity

The force of attraction between two objects

Define weight

The force of attraction when an object enters a gravitational field

Define kinetic energy

The energy that an object possesses due to its motion

Kinetic energy =

1/2 x mass x (velocity)^2

Define efficiency

Proportion of energy supplied that is transferred into useful energy output

Efficiency =

Useful energy output / total energy input

Elastic potential energy =

1/2 x spring constant x (extension)^2

Power =

work done / time

Force = (ke)

spring constant x extension

What is a spring constant?

A measure of the stiffness of a spring

What is the limit of proportionality?

The point beyond which Hooks Law is no longer true when stretching a material

Momentum =

mass x velocity

(In a closed system) the total momentum before an event =

the total momentum after the event

Define closed system

A system with no energy flow in or out / no external resultant forces acting on the system

resultant force =

change in momentum / time taken

spring constant unit

n/m

Why does opening a parachute slow down a skydiver?

increased surface area increases air resistance

What is the relationship between acceleration and mass?

Acceleration and mass are inversely proportional

What is the relationship between acceleration and force?

Acceleration and force are directly proportional

What goes on the x-axis of a distance/time graph?

time

acceleration=

change in velocity/time

Is weight a vector or scalar quantity?

Vector

The size of the air resistance is dependent on the object's...

surface area and velocity

What is the gradient on a distance-time graph?

Speed

How do you find the speed on an acceleration curve?

Draw a tangent and find its gradient

What does a curve mean on a velocity-time graph?

A change of acceleration

What does a straight line mean on a distance-time graph?

Stationary

What does a curve mean on a distance-time graph?

Acceleration or deceleration

What does a straight line mean on a velocity-time graph?

Constant velocity

What does the gradient of a velocity-time graph mean?

Acceleration

acceleration=

change in velocity/time

2as=

v^2 - u^2

As the velocity of a falling object increases, the air resistance:

increases

On a velocity / time graph, the distance travelled is shown by:

the area under the curve

momentum (p)=

mass x velocity

Define pressure

Force per unit area

Pressure in a fluid=

density x depth x gravitational field strength

What is Pascal's Law?

A change in pressure at any point within an incompressible fluid is transmitted equally throughout the fluid.

What is the condition for floating?

The object is less dense than the liquid.

What is upthrust?

Weight of fluid displaced

Define altitude

height above sea level

What causes air pressure?

Collisions of particles on a surface

What is air density dependant upon?

The weight of air above a surface

What happens to the weight of air if height decreases?

It decreases

stopping distance =

thinking distance + braking distance

thinking distance =

speed x reaction time

Define braking distance

the distance travelled by a car while braking

1/2 x mass x initial speed =

braking force x distance

force =

change in momentum / time

On a mountain, where is air pressure lowest?

The top

What is weight measured in?

Newtons

The gradient of a distance / time graph tells us:

speed

What is inertia?

tendency for an object to continue in its state of rest

Define a moment

The turning effect of a force

Moment=

Force x perpendicular distance from pivot

What is the unit for moments?

Newton metres (Nm)

Define centre of mass

the point where the mass appears to be concentrated

Spring constant units

N/m

Spring constant=

force/extension

Define braking force

The frictional force between brake blocks and the wheel rims

Factors affecting braking distance

Road condition, tyre condition,

The formula for pressure in a liquid is:

pressure = depth x gravitational field strength x density

A vehicle drives twice as fast. What happens to the braking distance?

Increases by 4 times

Define thinking distance

The distance the vehicle travels during the drivers reaction time

What could affect thinking distance?

Tiredness, distraction, alcohol or drugs

State the principles of moments

The sum of clockwise moments = the sum of anticlockwise moments for a system in equilibrium

What is the necessary condition for equilibrium?