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What is a vector quantity?
A quantity with magnitude (size) and direction
What examples are there of vector quantities?
Any force, velocity, displacement, acceleration, momentum
What is a scalar quantity?
A quantity with magnitude (size) only
What examples are there of scalar quantities?
Speed, distance, mass, temperature, time
How are vectors represented in a diagram?
With an arrow
How is the magnitude and direction of a force represented in a vector diagram?
The length represents the size of the quantity and the arrowhead the direction
What is a force?
A push or pull acting on an object
What is a contact force?
A force exerted when the objects are physically touching
What examples are there of contact forces?
Friction, air resistance, tension, normal contact force
What is a non-contact force?
A force exerted on objects that are physically separated
What examples are there of non-contact forces?
Magnetic force, gravitational force, electrostatic force
What happens when two objects interact?
A force is produced on both objects
What is an interaction pair?
Forces that are equal in size and opposite in direction
Which of Newton's Laws of motion is defined by an interaction pair?
Third law
What is a gravitational force?
An attraction force that acts between masses
When do we notice a gravitational force?
When one of the masses is very, very big, like a planet or star
What is mass?
The amount of matter an object is made of
What is the standard unit of mass and its unit symbol?
Kilograms, kg
What is weight?
A force acting on an object due to gravity
What is the unit for weight and all other forces and the unit symbol?
Newton, N
What does the weight of an object depend on?
The strength of the gravitational field and the mass of an object
What is meant by the term "centre of mass"?
An assumption that identifies a single point on object where the whole mass is concentrated
What is the relationship between weight and mass, when gravity is constant?
They are directly proportional
How is weight measured, practically?
Using a calibrated spring balance (a newtonmeter)
What is a free body diagram?
A diagram that shows all of the forces acting on an object
How are forces represented on a free body diagram
With an arrow, the length represents the size of the force and the arrowhead the direction of the force. (arrows always point away from the object)
What is a resultant force?
The overall force acting on an object
What happens when a resultant force moves an object?
Energy is transferred between energy stores and work is done
What does "resolving" a force mean?
Splitting a force into its horizontal and vertical components
What is true of the forces on an object that is in equilibrium?
Forces are balanced or there is an overall resultant force of zero
What three deformations can happen to an elastic object when forces are applied?
Stretching, compressing and bending
What is an elastic deformation?
The object will return to its original size and shape when forces are removed
What is an inelastic deformation?
One in which the object will not return to its original size and shape when forces are removed
Give two examples of elastic objects
A spring and a sponge
What type of energy is stored in a stretched spring?
Elastic potential energy
How do you calculate the extension of a spring?
Length of spring with force applied - original length of spring
How is the extension of a spring related to the force added?
Extension is directly proportional to the force added (up to a limit)
What does the spring constant depend on?
The stiffness of the spring
If you increase the stiffness of a spring what happens to the size of the spring constant?
It increases
How can you calculate the spring constant from a force-extension graph?
Calculate the gradient of the linear part (straight part) of the graph
On a force-extension graph, what does a steeper line represent?
A stiffer spring with a larger spring constant
When measuring a spring with a ruler, why must the ruler be parallel?
To increase the accuracy of the reading
When reading a vertical scale, what is meant by a parallax error?
The reading changes depending on where you are looking from
How do you prevent a parallax error from occurring?
Always read the measurement at eye level
Give two reasons to do a pilot or preliminary experiment
To find an appropriate interval size for the independent variable i.e one that gives measurable results. To check that the method works.
What type of quantity is distance?
Scalar
What type of quantity is displacement?
Vector
How is displacement different to distance?
Displacement is a vector quantity, measuring the distance and direction in a straight line from the starting point
What is the difference between speed and velocity?
Speed is a scalar quantity and velocity is a vector quantity
What two quantities do you need to measure to calculate speed?
Distance travelled and time taken
What symbol is used to represent distance?
s
What is the standard unit and unit symbol of distance?
Metres, m
What symbol is used to represent speed (velocity) and
v
What is the standard unit and unit symbol of velocity?
Metres per second, m/s
Why are most speeds said to be average speeds?
Objects rarely travel at a constant speed, they speed up and slow down.
What is the typical average speed for a person walking?
1.5 m/s
What is the typical average speed for a person running?
3.0 m/s
What is the typical average speed for a person cycling?
6 m/s
What is the typical average speed for a car?
25 m/s
What is the typical average speed for a train?
55 m/s
What is the typical average speed for a plane?
250 m/s
What is the speed of sound in air?
330 m/s
What is meant by acceleration?
Change in velocity in a certain amount of time
What happens to an objects velocity when it is travelling in a circle?
It is constantly changing
Why is travelling at a constant speed in a circle considered to be an example of constant acceleration?
Velocity is constantly changing due to the direction constantly changing
What is the standard unit and unit symbol for acceleration?
Metres per second squared, m/s2
What is meant by uniform acceleration?
constant acceleration
What is the acceleration due to gravity near the Earth's surface?
9.8 m/s2
On a distance-tine graph what does a straight line with a gradient represent?
Constant speed
What does a horizontal line on a distance-time graph represent?
The object is stationary
What does a curve represent on a distance-time graph?
Acceleration or deceleration
How can you calculate the acceleration from a curve on a distance-time graph?
Draw a tangent to the curve and calculate the gradient
On a velocity-time graph what does a straight line with a gradient represent?
Constant acceleration
What does a horizontal line on a velocity-time graph show?
Constant speed
What is different about the lines on a velocity-time graph which show acceleration and deceleration?
Acceleration is a line moving up the graph, deceleration is a line moving down the graph
How do you use a velocity-time graph to calculate the distance travelled by an object?
Calculate the area under the graph
Which force always acts in the opposite direction to motion?
Friction
What other name is given to the force of friction due to objects moving through a fluid?
Drag
When an object speeds up, what happens to the friction/drag force?
Increases
How can you reduce the effect of drag on a moving object?
Make it more streamlined
What force causes a falling object to accelerate?
Gravity
What force acts against gravity?
Drag/friction
What is meant by the terminal velocity of a falling object?
Maximum constant velocity
When does a falling object reach terminal velocity?
When the weight of the object is equal to the force of drag so the resultant force is zero
Why do objects fall at different speeds on earth when they have the same acceleration force due to gravity?
Friction forces due to air resistance depends on the shape and surface area of the object
State Newton's First Law
A resultant force is needed to make an object start moving, speed up, slow down or change direction.
What are the two possible conditions of an object with a resultant force of zero?
It must be stationary or moving at a constant velocity
State Newton's Second Law
The acceleration of an object is directly proportional to the force applied
What is inertia?
The tendency of an object to continue in their state of rest or of uniform motion
What is inertial mass and how is it calculated?
Measure of how difficult it is to change the velocity of an object, m= F ¸a
State Newton's Third Law
Whenever two objects interact, the forces they exert on each other are equal and opposite
What symbol represent 'approximately'
̴
What is meant by the "Stopping Distance" of a car?
The total distance travelled by a car in an emergency
State the two components of the total stopping distance of a car
Thinking distance and braking distance
What is the thinking distance?
The distance a car travels between seeing a hazard and the brakes being applied (the drivers reaction time)
What does typical human reaction time range between?
0.2s to 0.9s
What two key factors affect the thinking distance of a car?
The speed the car is travelling and the reaction time of the driver
What factors will increase the time it takes for a driver to react?
Alcohol, distractions, tiredness
What factors will increase the braking distance of a car?
Worn tyres, poor brakes, slippery roads (wet or icy)
What happens to the overall stopping distance as speed increases?
It increases
