Summative Practical: Motion down an Incline Plane In the next lesson, your task will be to perform an experiment to investigate the motion of a ball rolling down an incline plane. For an incline of 30°, the expected relationship between the distance travelled by the ball rolling down the incline () and the time () taken to travel this distance is: = 2.45 2 . (1) This experiment is to be conducted in groups of 2 or 3, however the experimental write-up and discussion of results will be done independently. You will have 2 hours to complete the experiment, with the write-up to be done in the booklet provided. This booklet must be handed up at the end of the lesson. There will also be marks assigned to safe and effective use of equipment, positive and effective teamwork, both of which the teacher will assess during the experimentation stage, and effective communication skills determined from the responses to the questions in the practical booklet. Preparation: First individually read the introduction and answer the questions in part (a). Then with your partner(s) briefly consider how you will undertake the experiment by identifying the independent and the dependent variables in order to verify the relationship above. Your answers to parts (a) will be collected at the beginning of the practical session. Complete your group design on a separate piece of paper as this will assist you in completing the investigation. Introduction For an object falling under the influence of gravity near the Earth’s surface, the gravitational force is effectively constant leading to a constant acceleration we call , the acceleration due to gravity. As we have constant acceleration, if the object starts at rest, then the distance travelled during a time is given by: = 1 2 2 . In this practical we shall consider the situation in which a ball rolls down an incline plane. This is a similar problem to that of the falling object, however in this case the ramp provides an additional force (the normal force which is perpendicular and away from the ramp). To understand the resulting motion, we resolve the force due to gravity into components along the ramp and perpendicular to the ramp. In doing this we find that the normal force completely cancels with the component of gravity perpendicular to the ramp, resulting in no net force in the perpendicular direction. However, the component of gravity along the ramp is unbalanced and so there is a net force in this direction. Working through the trigonometry, we can show that the magnitude of this force is: = sin . Using Newton’s second law we know that: = ⇒ = sin . Therefore, if the object starts at rest, the distance travelled down the incline plane during a time is given by: = 1 2 ( sin ) 2 . sin = cos
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Summative Practical: Motion down an Incline Plane
In the next lesson, your task will be to perform an experiment to investigate the motion of a ball rolling down an
incline plane. For an incline of 30°, the expected relationship between the distance travelled by the ball rolling down
the incline (𝑠) and the time (𝑡) taken to travel this distance is:
𝑠 = 2.45 𝑡2 . (1)
This experiment is to be conducted in groups of 2 or 3, however the experimental write-up and discussion of results
will be done independently. You will have 2 hours to complete the experiment, with the write-up to be done in the
booklet provided. This booklet must be handed up at the end of the lesson. There will also be marks assigned to
safe and effective use of equipment, positive and effective teamwork, both of which the teacher will assess during
the experimentation stage, and effective communication skills determined from the responses to the questions in
the practical booklet.
Preparation: First individually read the introduction and answer the questions in part (a). Then with your partner(s)
briefly consider how you will undertake the experiment by identifying the independent and the dependent variables
in order to verify the relationship above.
Your answers to parts (a) will be collected at the beginning of the practical session. Complete your group design on
a separate piece of paper as this will assist you in completing the investigation.
Introduction
For an object falling under the influence of gravity near the Earth’s surface, the gravitational force is effectively
constant leading to a constant acceleration we call 𝑔, the acceleration due to gravity. As we have constant
acceleration, if the object starts at rest, then the distance travelled during a time 𝑡 is given by:
𝑠 =1
2𝑔𝑡2 .
In this practical we shall consider the situation in which a ball rolls down an incline plane. This is a similar problem
to that of the falling object, however in this case the ramp provides an additional force (the normal force which is
perpendicular and away from the ramp). To understand the resulting motion, we resolve the force due to gravity
into components along the ramp and perpendicular to the ramp. In doing this we find that the normal force
completely cancels with the component of gravity perpendicular to the ramp, resulting in no net force in the
perpendicular direction. However, the component of gravity along the ramp is unbalanced and so there is a net
force in this direction.
Working through the trigonometry, we can show that the magnitude of this force is:
𝐹𝑥 = 𝑚𝑔 sin 𝜃 .
Using Newton’s second law we know that:
𝐹𝑥 = 𝑚𝑎𝑥
⇒ 𝑎𝑥 = 𝑔 sin 𝜃 .
Therefore, if the object starts at rest, the distance travelled down the incline plane during a time 𝑡 is given by:
𝑠 =1
2(𝑔 sin 𝜃)𝑡2 .
𝑚𝑔 sin 𝜃
𝑥
𝑦
𝜃
𝐹𝑁
𝐹𝑔 = 𝑚𝑔
𝑚𝑔 cos 𝜃 𝜃
Part (a): Individual Questions
In this practical, we shall verify this relationship by considering the motion of a solid ball bearing rolling down an
incline plane.
1) Give a brief explanation as to why you would expect the forces in the direction perpendicular to the ramp
to cancel. (Hint: What would happen if the forces did not cancel each other?) (KU1)
Practical and Collaborative Skills Assessment Sheet:
I3: Manipulates apparatus and technological tools carefully and highly effectively to implement well-organised, safe, and ethical investigation procedures.
A3: Demonstrates initiative in applying constructive and focused individual and collaborative work skills.
Indicator A (4) B (3) C (2) D (1) E (0)
I3 Uses equipment safely,
Recognises hazards and takes required precautions
Ability to problem solve (issues with practical)
A3 Cooperates with all group members
Shows initiative
Uses time effectively
Logical and systematic approach to the undertaking of the experiment.