# Dynamics

- use of F = ma when mass is constant
- one-and two-dimensional motion under constant force
- independent effect of perpendicular components with uniform acceleration
- projectile motion

Although most textbooks will list the relationship as F=ma, it is much easier for students to appreciate it as a=F/m. In this form the acceleration is clearly the consequence of a (resultant) force acting on a mass; much clearer.

The ideas in this topic will lead towards momentum, which most students will be familiar with from GCSE. The momentum and impulse equations are arguably some of the hardest they will deal with before A level so it is probably worth spending some time consolidating their understanding of simple forces on a body before moving on. (Newton's work was first expressed in terms of momentum, not acceleration.)

You will be building on their previous work into forces as vectors. In most cases a constant acceleration is due to the weight of an object (ie because of gravity) or a constant force such as friction. For most students drawing a free-body diagram with labelled forces is a good starting point. This narrative approach makes it less likely that the calculations will go awry unnoticed.

Whilst this list provides a source of information and ideas for experimental work, it is important to note that recommendations can date very quickly. Do NOT follow suggestions which conflict with current advice from CLEAPSS or recent safety guides. eLibrary users are responsible for ensuring that any activity, including practical work, which they carry out is consistent with current regulations related to Health and Safety and that they carry an appropriate risk assessment. Further information is provided in our Health and Safety guidance.

### Investigating Newton's Second Law of Motion

This web link takes you to a comprehensive set of instructions to investigate Newton's second law of motion. The basic experiment can be done differently with stopwatches and metre rules or ticker timers; in this case a generic set of instructions is given for use with light gates and data loggers. Regardless of which choice of data loggers you have, you should obtain a good set of data to test the equation.

### F=ma in a Helicopter

This is a straightforward demonstration which provides some surprising insights for students about the effect of force, not on a helicopter but on an object hanging below it. Guidance is included which suggests some useful questions and prompts for your class. Very little equipment is needed but it may be an interesting exercise to ask students how they could change the method to collect quantitative data.

### Forces in 1 Dimension

An interactive simulation exploring the forces at work when you try to push a filing cabinet. Users can create an applied force and see the resulting friction force and total force acting on the cabinet. Charts show the forces, position, velocity, and acceleration against time. A free body diagram of all the forces (including gravitational and normal forces) can also be viewed.

### Mechanics 1

Many of the approaches we teach will also be covered by students studying maths - this is why most departments routinely record who is and isn't doing A level maths. If it's possible to discuss timing and terminology with colleagues you can be clear with students about the occasional need for different language.

This resource may be a useful starting point; it is a textbook intended for a mathematical approach to Newtonian mechanics. Some sections may be used as they are, such as the summary problems from page 113 of the PDF. If you use extracts with students, ensure they are clear about what they need for their exams and what (such as derivations) may be superfluous. In particular, remind students that calculus (differentiation and integration) will not be required in A level physics.

### Perpendicular Components of Motion *suitable for home teaching*

A brilliant website article looking at the independence of perpendicular components of motion.

### Episode 207: Projectile Motion

Students will resist the idea that vertical and horizontal forces act independently on a body. Part of this goes back to the misconception that a thrown object has a 'forwards' force acting while it is moving; you may find it useful to ask them to draw the forces acting on a paper plane in flight, compared with those acting on a powered model plane.

The activities in this resource include several demonstrations and practicals to reinforce the idea that a parabola is used to describe the motion of a thrown or fired object. Explanations of the classic monkey and hunter example below are also given.

### Monkey and Hunter

A classic experiment with an outcome that often surprises students. Setting it up in the lab can be problematic, as the apparatus often sees little use, but this video gives suggestions about useful tips before and during the demonstration. As with the guinea and feather, simulations do not have the same impact, but a version of the video is available that can be used with students if needed.

The slow-motion scene at the finish is particularly useful and if possible, this is something you should aim to recreate in your setting. A high frame-rate and some simple annotation will give students something that illustrates the independance of vertical and horizontal motion nicely.

### Creating a 'Rockets in Motion' Project

This project summary explains how colleagues in several school departments, including physics, worked together to use projectiles to teach several linked STEM concepts. This would be an excellent start to an after-school STEM club, with students of different ages considering different aspects of the rocket motion.

### Radar: seeing the unseen

This activity booklet uses the real life context of air traffic control using radar signals to identify the position of an aeroplane that students act out. It provides them with an opportunity to use their knowledge of waves and speed = distance / time to calibrate and calculate the distance a plane is from the radar. This will aid their working scientifically skill base as well as providing them with how physics is used day to day.