P4 Flashcards
What is the formula for speed?
Distance traveled (m) / time taken (s)
What is speed measured in?
m/s
What is it called if you measure average speed over a very short time period?
Instantaneous speed.
What is the displacement of an object?
The distance from its start point to the straight line?
How is displacement expressed?
As a distance with a direction.
Are displacement and velocity scalar or vector quantities?
Both vector.
What is the velocity of an object?
It’s speed in a certain direction.
What is the formula for average velocity?
displacement/time taken.
What is a distance-time graph used for?
To visualize a journey.
In a distance-time graph, what is plotted against the y-axis and what is plotted against the x-axis?
Y-axis : the time
X -axis: the distance travelled
In a distance-time graph, what does a horizontal line mean?
The vehicle is stationary.
In a distant-time graph, what is the gradient of the line equal to?
The speed.
In a distant-time graph, the steeper the gradient…
the faster the speed.
In a distant-time graph, what does a curved line mean?
The speed is changing.
In a distant-time graph, what does it mean if a curve is getting steeper?
the vehicles speed is increasing.
What is a displacement time-graph used for?
To visualize return journeys.
What is acceleration?
The rate at which the speed of an object increases.
What is acceleration measured in?
m/s^2
Acceleration=
change in speed (m/s) / time taken (s)
What is deceleration?
When an object slows down.
What has to be acting on an object to cause acceleration (or deceleration)?
A force.
When the net or overall force is zero, the acceleration is…
zero.
What is a speed-time graph used for?
to show the changes in speed during a journey.
In a speed-time graph, what is plotted on the x-axis and what is plotted on the y-axis?
Y axis: speed
X axis: time
In a speed-time graph, what does a horizontal line mean?
constant speed.
What does a velocity-time graph show?
the direction in which an object is travelling?
What does a positive and negative velocity mean?
Negative velocity: the object is travelling in a negative direction.
Positive velocity: the object is travelling in a certain direction
What is a force?
A push or pull which acts between two objects.
Forces always act in…
pairs.
What does a repulsive force do?
Pushes objects apart.
What does an attractive force do?
Pulls objects towards each-other.
Are forces vector or scalar quantities?
Vector.
How is force represented on a diagram?
With an arrow.
What is friction?
A force that acts between two surfaces.
What does the side of the friction force depend on?
- the roughness of the surfaces (rougher surfaces give more friction).
- how hard the surfaces are pushed together (the heavier the object the more friction).
What is limiting friction?
When the friction reaches a maximum value.
Why do you need friction to walk?
When you walk your feet push against the friction, pushing your foot forwards.
What is resultant force?
The total or overall force acting on an object.
What happens when the resultant force is equal to 0?
the forces are balanced.
What speed do objects accelerate to the ground at as a result of gravity?
9.8 m/s^2.
What is the upwards force that slows down falling objects?
Air resistance or drag?
What is drag?
The force that acts in the opposite direction to the speed.
Drag force increases as…
the speed of the object increases.
The larger the surface area of the object…
the larger the drag force.
What is terminal velocity?
When the constant maximum speed is reached by a falling object.
What does the size of the force depend on?
- the mass of the object.
- the speed of the object.
- the duration of the impact.
What are car safety devices, e.g. air bags, crumple zones and seat belts, designed for?
to reduce the impact time, thus reducing the force in a collision.
What is the momentum formula?
Mass x velocity
What is the formula for change in momentum?
resultant force x time for which it acts.
What is the formula for force?
Change in momentum / time taken.
What is work(done)?
The energy used by the movement of a force?
What is energy and work measured in?
Joules (J).
What is the formula for work done?
Force x Distance moved in the direction of the force
What is the same as work done?
Amount of energy transferred.
When you lift an object…
you do work against gravity.
When you life an object, the work done is transferred to…
GPE.
What is the formula for Kinetic energy?
1/2 x mass x velocity^2.
What is the formula for Work done?
force x distance moved.
What is the principle of the conservation of energy?
When there are no resistive forces the total energy remains constant.
Energy cant be either created or destroyed…
it can only be transferred/(change form).
