Thick and soft to offer ________ created by a person landing.
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Straight lines
________ are constant (aka uniform) acceleration (steep slope is large acceleration or deceleration)
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velocity time graph
The area underneath a(n) ________ represents the displacement of the object.
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contact time
Since force is equal to the rate of change in momentum, the force of an impact in a vehicle collision can be decreased by increasing the ________ over which the collision occurs.
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Acceleration
________ is the rate of change of velocity.
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Displacement
________ is the distance travelled /the distance moved.
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Momentum
________ does depend on the direction of the objects travel (it can be positive or negative)
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Newtons first law
________ is that objects remain at rest, or move with a constant velocity unless acted upon by a resultant force.
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Momentum
________ is what keeps objects moving in the same direction, which makes it difficult to change direction without large changes in ________.
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straight line
The ________ means that there is a constant speed.
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When there is uniform acceleration, you can use the formula v^2
u^2 = 2as to calculate velocity, distance and acceleration
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There is a simple equation for this
total momentum before the collision = total momentum after the collision
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What are the 2 effects of forces?
Acceleration - change in speed, change in direction
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Deformation - change in size, change in shape
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Is force a scalar or a vector?
Vector
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What is the unit for force and what can it be measured with?
Newtons - spring balance, newton-meter
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What is the definition of weight?
The weight of a body is the force of gravity on it.
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What exerts gravity?
Any body with a mass
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What forces decrease with distance?
Magnetic, gravitational, and electrostatic forces
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What is the force of gravity on Earth?
9.8 N/kg
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State Hooke's Law:
Extension is directly proportional to stretching force until limit of proportionality/elastic limit is reached.
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What is the Hooke's Law formula?
k = F/x
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What is the spring constant?
Force needed to cause unit extension, spring constant increases as it becomes more difficult to stretch/extend a spring.
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What is the definition of resultant force?
A single force that has the SAME effect of all the other forces combined
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What is the parallelogram law?
If 2 forces are represented in size and direction by the sides of a parallelogram drawn from the point the resultant force is represented in size and direction by the diagonal of a parallelogram drawn from the point.
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What is the difference between scalars and vectors?
Scalar - only has a magnitude, eg. mass, speed, added via arithmetic
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Vector - has a magnitude and a direction, eg. force, velocity, added geometrically
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Define friction:
Force between two surfaces that impedes motion and results in heating (necessary for human movement - slip otherwise)
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What happens to the temp. of the bodies in contact under the force of friction?
Temp. increases
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How can friction be increased?
Increase the force pushing the objects together, roughen surfaces
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What is Newton's first law?
An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.
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What is Newton's second law?
Force = mass x acceleration
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What is Newton's third law?
If body A exerts a force on body B, body B exerts an equal and opposite force on body A
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What is the weight formula?
w = mg
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How does an object reach terminal velocity?
As an object falls through the air the air resistance increases as speed increases = reducing its acceleration, when air resistance = weight resultant force is 0, object falls at a constant TERMINAL velocity
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What is the formula for momentum?
mass of body x velocity
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What is the unit for momentum?
Newton second (kg x m/s)
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What is the equation relating momentum, force, and time taken?
force = change of momentum divided by time taken = rate of change of momentum
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What is an impulse? What is it sometimes represented by?
something that changes the momentum of an object, Ft
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What letter is used to represent momentum sometimes?
p
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What is another one of saying two bodies act on each other?
Two bodies interact
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What is momentum useful for?
explosions/collisions
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What is the principle of the conservation of momentum?
When two bodies interact (e.g. collision), the total momentum of the bodies remains constant - provided that no external forces act (e.g. friction)
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What is the equation for the impulse?
Ft (impulse) = final momentum - initial momentum
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What is the turning effect of a force?
moment of a force
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What can a body attached to a pivot not do?
Translate - one point always remains in the same place (point attached to pivot)
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What is the unit of a moment?
N m (Newton meter)
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What does a moment depend on? (4)
size of force
direction of force
point of action of force
position of pivot
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What is the law of moments?
When an object is in equilibrium the sum of the clockwise moments is equal to the sum of the anticlockwise moments about the same point.
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When is there no net moment on a body?
When it is at equilibrium!
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Define equilibrium
A body is at equilibrium if it does no rotations or translations
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What is a lever?
Any device which can turn about a pivot
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How can you confirm a body is at equilibrium?
Check that the resultant force is zero and then ensure the law of moments applies to one other point of your choice.
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What is the center of mass/center of gravity?
From the of view of gravity a body behaves as if its entire mass were concentrated at one point called the center of mass/gravity.
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How do you find the center of mass in a regularly shaped body with a CONSTANT density throughout? For example a triangle?
It is at its center, the geometrical center of a triangle = point of intersection of 3 median lines
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Can the center of mass of an object lie outside the object?
Yes!
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How is the center of mass of an irregularly shaped body determined?
Determined with a plumb line.
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- hang object at point A so it can swing freely
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- when it comes to rest hang a weight from point A
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- center of mass is along the line along the string holding the mass from point A, draw the line
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- repeat with another point - the center of mass is where the 2 lines intersect
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When does an object topple?
An object topples when a vertical line drawn from the center of mass does not go through the base of the object
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How do you increase the stability of an object?
Increasing width of the base, lower the center of mass
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